Method for managing radio resources in communication system and apparatus for the same

ABSTRACT

A beam management method, performed by a terminal in a communication system, includes receiving a control message including at least one parameter used for beam management from a first base station; performing a monitoring operation on a first beam configured between the first base station and the terminal based on the at least one parameter; detecting a beam problem in the first beam based on the monitoring operation; and in response to determination that the beam problem is detected in the first beam, performing a recovery operation on the first beam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priorities to Korean Patent Applications No.10-2017-0124876 filed on Sep. 27, 2017, No. 10-2017-0147569 filed onNov. 7, 2017, No. 10-2018-0017157 filed on Feb. 12, 2018, No.10-2018-0084630 filed on Jul. 20, 2018, No. 10-2018-0091430 filed onAug. 6, 2018, and No. 10-2018-0103454 filed on Aug. 31, 2018 in theKorean Intellectual Property Office (KIPO), the entire contents of whichare hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a technique for managing radioresources, and more particularly, to a beam management technique forensuring terminal mobility.

2. Description of Related Art

A communication system (hereinafter, an ‘integrated communicationsystem’) using a higher frequency band (e.g., a frequency band of 6 GHzor higher) than a frequency band (e.g., a frequency band lower below 6GHz) of a long term evolution (LTE) based communication system (or, aLTE-A based communication system) is being considered for processing ofsoaring wireless data. The integrated communication system may comprisean access network, an Xhaul network, and a core network, and the Xhaulnetwork may support communications between the access network and thecore network.

The reception performance of a signal may deteriorate due to path lossof a radio wave and reflection of the radio wave in such the highfrequency band (e.g., a frequency band of 6 GHz or higher), and a smallbase station supporting smaller cell coverage than that of a macro basestation can be introduced into the integrated communication system inorder to solve this problem. In the integrated using a wired backhaullink, in which case an initial investment cost, management cost, or thelike of the integrated communication system may be increased.

Meanwhile, the integrated communication system may comprise the smallbase station performing all the functions of a communication protocol(e.g., a remote radio transmission and reception function, a basebandprocessing function), a plurality of transmission reception points(TRPs) performing the remote radio transmission and reception functionamong the functions of the communication protocol, a baseband unit (BBU)block performing the baseband processing function among the functions ofthe communication protocol, and the like. The TRP may be a remote radiohead (RRH), a radio unit (RU), or the like. The BBU block may include atleast one BBU or at least one digital unit (DU). The BBU block may bereferred to as a ‘BBU pool’, a ‘centralized BBU’, or the like. One BBUblock may be connected to a plurality of TRPs, and perform the basebandprocessing function on signals received from the plurality of TRPs andsignals to be transmitted to the plurality of TRPs. In the integratedcommunication system, the small base station may be connected to thecore network using a wireless backhaul link (e.g., a wireless backhaullink constituting the Xhaul network), and the TRP may be connected tothe BBU block using a wireless fronthaul link (e.g., a wirelessfronthaul link constituting the Xhaul network).

In the above-described integrated communication system, a beammanagement procedure, a radio link management procedure, and the likeare required to ensure mobility of communication nodes (e.g.,terminals).

SUMMARY

Accordingly, embodiments of the present disclosure provide beammanagement methods for ensuring mobility of terminals in a communicationsystem.

In order to achieve the objective of the present disclosure, a beammanagement method performed by a terminal in a communication system maycomprise receiving a control message including at least one parameterused for beam management from a first base station; performing amonitoring operation on a first beam configured between the first basestation and the terminal based on the at least one parameter; detectinga beam problem in the first beam based on the monitoring operation; andin response to determination that the beam problem is detected in thefirst beam, performing a recovery operation on the first beam.

The terminal may include a physical (PHY) layer, a medium access control(MAC) layer, and a radio resource control (RRC) layer, and themonitoring operation and the recovery operation may be controlled by theMAC layer included in the terminal.

When a plurality of beams are configured between the first base stationand the terminal, the monitoring operation and the recovery operationmay be performed on a beam-by-beam basis.

In response to determination that the terminal is not synchronized withthe first base station during a period indicated by the at least oneparameter, the beam problem may be determined as detected in the firstbeam.

The PHY layer included in the terminal may determine whether theterminal is synchronized with the first base station, information onwhether the terminal is synchronized with the first base station may betransmitted from the PHY layer to the MAC layer included in theterminal, and the MAC layer may determine the beam problem based on theinformation on whether the terminal is synchronized with the first basestation.

In response to determination that a reception quality of referencesignals received through the first beam during a period indicated by theat least one parameter is equal to or less than a reference value, thebeam problem may be determined as detected in the first beam.

The control message may be a control channel of a physical layer (e.g.,downlink control information (DCI)), a MAC control message, or an RRCmessage.

The beam management method may further comprise, in response todetermination of a beam recovery failure by the beam recovery operation,performing a reconfiguration operation on another beam excluding thefirst beam among a plurality of beams supported by the first basestation.

The reconfiguration operation may be performed in a MAC layer includedin the terminal or an RRC layer included in the terminal.

The beam management method may further comprise, in response todetermination of a radio link configuration failure by thereconfiguration operation, performing a re-establishment operation of aradio link with a second base station other than the first base station.

When a plurality of beams are configured between the first base stationand the terminal and all of reconfiguration operations on the pluralityof beams fail, the radio link configuration failure may be determined.

The re-establishment operation of the radio link may be performed by anRRC layer included in the terminal.

In response to determination that the re-establishment operation of theradio link fails, an operational state of the terminal may transitionfrom an RRC_CONNECTED state to an RRC_INACTIVE state or an RRC_IDLEstate.

In order to achieve the objective of the present disclosure, a terminalsupporting a beam management operation in a communication system maycomprise a processor and a memory storing at least one instructionexecuted by the processor. Here, the at least one instruction may beconfigured to receive a control message including at least one parameterused for beam management from a first base station; perform a monitoringoperation on a first beam configured between the first base station andthe terminal based on the at least one parameter; detect a beam problemin the first beam based on the monitoring operation; and in response todetermination that the beam problem is detected in the first beam,perform a recovery operation on the first beam.

When a plurality of beams are configured between the first base stationand the terminal, the monitoring operation and the recovery operationmay be performed on a beam-by-beam basis.

In response to determination that the terminal is not synchronized withthe first base station during a period indicated by the at least oneparameter, the beam problem may be determined as detected in the firstbeam.

In response to determination that a reception quality of referencesignals received through the first beam during a period indicated by theat least one parameter is equal to or less than a reference value, thebeam problem may be determined as detected in the first beam.

The at least one instruction may be further configured to, in responseto determination of a radio link configuration failure by thereconfiguration operation, perform a re-establishment operation of aradio link with a second base station other than the first base station.

When a plurality of beams are configured between the first base stationand the terminal and all of reconfiguration operations on the pluralityof beams fail, the radio link configuration failure may be determined.

In response to determination that the re-establishment operation of theradio link fails, an operational state of the terminal may transitionfrom an RRC_CONNECTED state to an RRC_INACTIVE state or an RRC_IDLEstate.

According to the embodiments of the present disclosure, one or morebeams can be configured between the base station and the terminal, andthe terminal may perform communications with the base station using theconfigured beams. When a beam problem is detected during thecommunications between the base station and the terminal, the terminalcan perform a recovery operation on the beam in which the beam problemis detected. When the recovery operation fails, the terminal can performa reconfiguration operation on another beam of the base station. Whenthe reconfiguration operation fails, the terminal can perform are-establishment operation of a radio link with another base station.Through the above-described beam management operation, a communicationservice can be seamlessly provided to the terminal, and mobility of theterminal can be efficiently controlled. Therefore, the performance ofthe communication system can be improved.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure will become more apparent bydescribing in detail embodiments of the present disclosure withreference to the accompanying drawings, in which:

FIG. 1 is a conceptual diagram illustrating a first embodiment of acommunication system;

FIG. 2 is a block diagram illustrating a first embodiment of acommunication node constituting a communication system;

FIG. 3 is a conceptual diagram illustrating a second embodiment of acommunication system;

FIG. 4 is a conceptual diagram illustrating a first embodiment of anintegrated communication system;

FIG. 5 is a conceptual diagram illustrating a second embodiment of anintegrated communication system;

FIG. 6 is a conceptual illustrating a first embodiment of abeamforming-based communication method in a communication system;

FIG. 7 is a timing diagram illustrating a first embodiment of a beammanagement procedure in a communication system; and

FIG. 8 is a flow chart illustrating a first embodiment of a beammanagement procedure in a communication system.

DETAILED DESCRIPTION

While the present invention is susceptible to various modifications andalternative forms, specific embodiments are shown by way of example inthe drawings and described in detail. It should be understood, however,that the description is not intended to limit the present invention tothe specific embodiments, but, on the contrary, the present invention isto cover all modifications, equivalents, and alternatives that fallwithin the spirit and scope of the present invention.

Although the terms “first,” “second,” etc. may be used herein inreference to various elements, such elements should not be construed aslimited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and a second element could be termed a first element,without departing from the scope of the present invention. The term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directed coupled” to another element, there are nointervening elements.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of embodiments ofthe present invention. As used herein, the singular forms “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises,” “comprising,” “includes,” and/or “including,”when used herein, specify the presence of stated features, integers,steps, operations, elements, parts, and/or combinations thereof, but donot preclude the presence or addition of one or more other features,integers, steps, operations, elements, parts, and/or combinationsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by thoseof ordinary skill in the art to which the present invention pertains. Itwill be further understood that terms defined in commonly useddictionaries should be interpreted as having a meaning that isconsistent with their meaning in the context of the related art and willnot be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.To facilitate overall understanding of the present invention, likenumbers refer to like elements throughout the description of thedrawings, and description of the same component will not be reiterated.

Hereinafter, a communication system to which embodiments according tothe present disclosure will be described. However, the communicationsystems to which embodiments according to the present disclosure areapplied are not restricted to what will be described below. That is, theembodiments according to the present disclosure may be applied tovarious communication systems. Here, the term ‘communication system’ maybe used with the same meaning as the term ‘communication network’.

FIG. 1 is a conceptual diagram illustrating a first embodiment of acommunication system.

Referring to FIG. 1, a communication system 100 may comprise a pluralityof communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2,130-3, 130-4, 130-5, and 130-6. Also, the communication system 100 mayfurther include a core network. The core network supporting 4Gcommunication (e.g., long term evolution (LTE) and LTE-advanced (LTE-A))may comprise a serving gateway (S-GW), a packet data network (PDN)gateway (P-GW), a mobility management entity (MME), and the like. Thecore network supporting 5G communication (e.g., new radio (NR)) maycomprise a user plane function (UPF), an access and mobility managementfunction (AMF), and the like. The S-GW may correspond to the UPF, andthe MME may correspond to the AMF. Thus, in the embodiments describedbelow, the S-GW may mean the UPF, the MME may mean the AMF, and theS-GW/MME may mean the UPF/AMF.

The plurality of communication nodes may support 4th generation (4G)communication (e.g., long term evolution (LTE), LTE-advanced (LTE-A)),5th generation (5G) communication, or the like. The 4G communication maybe performed in a frequency band below 6 gigahertz (GHz), and the 5Gcommunication may be performed in a frequency band above 6 GHz. Forexample, for the 4G and 5G communications, the plurality ofcommunication nodes may support at least one communication protocolamong a code division multiple access (CDMA) based communicationprotocol, a wideband CDMA (WCDMA) based communication protocol, a timedivision multiple access (TDMA) based communication protocol, afrequency division multiple access (FDMA) based communication protocol,an orthogonal frequency division multiplexing (OFDM) based communicationprotocol, an orthogonal frequency division multiple access (OFDMA) basedcommunication protocol, a cyclic prefix OFDM (CP-OFDM) basedcommunication protocol, a discrete Fourier transform spread OFDM(DFT-s-OFDM) based communication protocol, a single carrier FDMA(SC-FDMA) based communication protocol, a non-orthogonal multiple access(NOMA) based communication protocol, a generalized frequency divisionmultiplexing (GFDM) based communication protocol, a filter bankmulti-carrier (FBMC) based communication protocol, a universal filteredmulti-carrier (UFMC) based communication protocol, and a space divisionmultiple access (SDMA) based communication protocol. Each of theplurality of communication nodes may have the following structure.

FIG. 2 is a block diagram illustrating a first embodiment of acommunication node constituting a cellular communication system.

Referring to FIG. 2, a communication node 200 may comprise at least oneprocessor 210, a memory 220, and a transceiver 230 connected to thenetwork for performing communications. Also, the communication node 200may further comprise an input interface device 240, an output interfacedevice 250, a storage device 260, and the like. Each component includedin the communication node 200 may communicate with each other asconnected through a bus 270.

However, each component included in the communication node 200 may beconnected to the processor 210 via an individual interface or a separatebus, rather than the common bus 270. For example, the processor 210 maybe connected to at least one of the memory 220, the transceiver 230, theinput interface device 240, the output interface device 250, and thestorage device 260 via a dedicated interface.

The processor 210 may execute a program stored in at least one of thememory 220 and the storage device 260. The processor 210 may refer to acentral processing unit (CPU), a graphics processing unit (GPU), or adedicated processor on which methods in accordance with embodiments ofthe present disclosure are performed. Each of the memory 220 and thestorage device 260 may be constituted by at least one of a volatilestorage medium and a non-volatile storage medium. For example, thememory 220 may comprise at least one of read-only memory (ROM) andrandom access memory (RAM).

Referring again to FIG. 1, the communication system 100 may comprise aplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2, and aplurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6.Each of the first base station 110-1, the second base station 110-2, andthe third base station 110-3 may form a macro cell, and each of thefourth base station 120-1 and the fifth base station 120-2 may form asmall cell. The fourth base station 120-1, the third terminal 130-3, andthe fourth terminal 130-4 may belong to cell coverage of the first basestation 110-1. Also, the second terminal 130-2, the fourth terminal130-4, and the fifth terminal 130-5 may belong to cell coverage of thesecond base station 110-2. Also, the fifth base station 120-2, thefourth terminal 130-4, the fifth terminal 130-5, and the sixth terminal130-6 may belong to cell coverage of the third base station 110-3. Also,the first terminal 130-1 may belong to cell coverage of the fourth basestation 120-1, and the sixth terminal 130-6 may belong to cell coverageof the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1,and 120-2 may refer to a Node-B, a evolved Node-B (eNB), a gNB, anng-eNB, a base transceiver station (BTS), a radio base station, a radiotransceiver, an access point, an access node, a road side unit (RSU), aradio remote head (RRH), a transmission point (TP), a transmission andreception point (TRP), a flexible TRP (f-TRP), or the like. Also, eachof the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and130-6 may refer to a user equipment (UE), a terminal, an accessterminal, a mobile terminal, a station, a subscriber station, a mobilestation, a portable subscriber station, a node, a device, a devicesupporting internet of things (IoT) functions, a mountedmodule/device/terminal, an on-board unit (OBU), or the like.

Meanwhile, each of the plurality of base stations 110-1, 110-2, 110-3,120-1, and 120-2 may operate in the same frequency band or in differentfrequency bands. The plurality of base stations 110-1, 110-2, 110-3,120-1, and 120-2 may be connected to each other via an ideal backhaul ora non-ideal backhaul, and exchange information with each other via theideal or non-ideal backhaul. Also, each of the plurality of basestations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to thecore network through the ideal or non-ideal backhaul. Each of theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 maytransmit a signal received from the core network to the correspondingterminal 130-1, 130-2, 130-3, 130-4, 130-5, or 130-6, and transmit asignal received from the corresponding terminal 130-1, 130-2, 130-3,130-4, 130-5, or 130-6 to the core network.

Also, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1,and 120-2 may support a multi-input multi-output (MIMO) transmission(e.g., a single-user MIMO (SU-MIMO), a multi-user MIMO (MU-MIMO), amassive MIMO, or the like), a coordinated multipoint (CoMP)transmission, a carrier aggregation (CA) transmission, a transmission inunlicensed band, a device-to-device (D2D) communications (or, proximityservices (Prose)), or the like. Here, each of the plurality of terminals130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 may perform operationscorresponding to the operations of the plurality of base stations 110-1,110-2, 110-3, 120-1, and 120-2 (i.e., the operations supported by theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2). Forexample, the second base station 110-2 may transmit a signal to thefourth terminal 130-4 in the SU-MIMO manner, and the fourth terminal130-4 may receive the signal from the second base station 110-2 in theSU-MIMO manner. Alternatively, the second base station 110-2 maytransmit a signal to the fourth terminal 130-4 and fifth terminal 130-5in the MU-MIMO manner, and the fourth terminal 130-4 and fifth terminal130-5 may receive the signal from the second base station 110-2 in theMU-MIMO manner.

The first base station 110-1, the second base station 110-2, and thethird base station 110-3 may transmit a signal to the fourth terminal130-4 in the CoMP transmission manner, and the fourth terminal 130-4 mayreceive the signal from the first base station 110-1, the second basestation 110-2, and the third base station 110-3 in the CoMP manner.Also, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1,and 120-2 may exchange signals with the corresponding terminals 130-1,130-2, 130-3, 130-4, 130-5, or 130-6 which belongs to its cell coveragein the CA manner. Each of the base stations 110-1, 110-2, and 110-3 maycontrol D2D communications between the fourth terminal 130-4 and thefifth terminal 130-5, and thus the fourth terminal 130-4 and the fifthterminal 130-5 may perform the D2D communications under control of thesecond base station 110-2 and the third base station 110-3.

Meanwhile, in a communication system, a base station may perform allfunctions (e.g., remote radio transmission and reception function,baseband processing function, and the like) according to a communicationprotocol. Alternatively, the remote radio transmission and receptionfunction among all the functions according to the communication protocolmay be performed by a transmission reception point (TRP) (e.g., f-TRP),and the baseband processing function among all the functions accordingto the communication protocol may be performed by a baseband unit (BBU)block. The TRP may be a remote radio head (RRH), a radio unit (RU), atransmission point (TP), or the like. The BBU block may include at leastone BBU or at least one digital unit (DU). The BBU block may be referredto as a ‘BBU pool’, a ‘centralized BBU’, or the like. The TRP may beconnected to the BBU block via a wired fronthaul link or a wirelessfronthaul link. A communication system composed of a backhaul link and afronthaul link may be as follows. When a function-split technique of thecommunication protocol is applied, the TRP may selectively perform somefunctions of the BBU or some functions of a medium access control (MAC)or a radio link control (RLC) layer.

FIG. 3 is a conceptual diagram illustrating a second embodiment of acommunication system.

Referring to FIG. 3, a communication system may include a core networkand an access network. The core network supporting the 4G communicationsmay include an MME 310-1, an S-GW 310-2, a P-GW 310-3, and the like. Thecore network supporting the 5G communications may include AMF, UPF, orthe like. The access network may include a macro base station 320, asmall base station 330, TRPs 350-1 and 350-2, terminals 360-1, 360-2,360-3, 360-4, and 360-5, and the like. The macro base station 320 or thesmall base station 330 may be connected with an end node of the corenetwork via a wired backhaul. The TRPs 350-1 and 350-2 may support theremote radio transmission and reception function among all the functionsaccording to the communication protocol, and the baseband processingfunctions for the TRPs 350-1 and 350-2 may be performed by the BBU block340. The BBU block 340 may belong to the access network or the corenetwork. The communication nodes (e.g., MME, S-GW, P-GW, AMF, UPF, macrobase station, small base station, TRPs, terminals, and BBU block)belonging to the communication system may be configured identically orsimilarly to the communication node 200 shown in FIG. 2.

The macro base station 320 may be connected to the core network (e.g.,MME 310-1, S-GW 310-2, AMF, UPF, or the like) using a wired backhaullink or a wireless backhaul link, and provide communication services tothe terminals 360-3 and 360-4 based on a communication protocol (e.g.,4G communication protocol, 5G communication protocol). The small basestation 330 may be connected to the core network (e.g., MME 310-1, S-GW310-2, AMF, UPF, or the like) using a wired backhaul link or a wirelessbackhaul link, and may provide communication services to the terminal360-5 based on a communication protocol (e.g., 4G communicationprotocol, 5G communication protocol).

The BBU block 340 may be located in the MME 310-1, the S-GW 310-2, AMF,UPF, or the macro base station 320. Alternatively, the BBU block 340 maybe located independently of each the MME 310-1, the S-GW 310-2, AMF,UPF, and the macro base station 320. For example, the BBU block 340 maybe configured as a logical function between the macro base station 320and the MME 310-1 (or S-GW 310-2). The BBU block 340 may support theplurality of TRPs 350-1 and 350-2, and may be connected to each of theplurality of TRPs 350-1 and 350-2 using a wired fronthaul link or awireless fronthaul link. That is, the link between the BBU block 340 andthe TRPs 350-1 and 350-2 may be referred to as a ‘fronthaul link’.

The first TRP 350-1 may be connected to the BBU block 340 via a wiredfronthaul link or a wireless fronthaul link, and provide communicationservices to the first terminal 360-1 based on a communication protocol(e.g., 4G communication protocol, 5G communication protocol). The secondTRP 350-2 may be connected to the BBU block 340 via a wired fronthaullink or a wireless fronthaul link, and provide communication services tothe second terminal 360-2 based on a communication protocol (e.g., 4Gcommunication protocol, 5G communication protocol).

In the embodiments to be described below, a communication systemincluding an access network, an Xhaul network, and a core network may bereferred to as an ‘integrated communication system’. The communicationnodes (e.g., MME, S-GW, P-GW, AMF, UPF, BBU block, Xhaul distributedunit (XDU), Xhaul control unit (XCU), base station, TRP, terminal, andthe like) may be configured identically or similarly to thecommunication node 200 shown in FIG. 2. The communication nodesbelonging to the Xhaul network may be connected using an Xhaul link, andthe Xhaul link may be a backhaul link or a fronthaul link.

Also, the S-GW (or, UPF) of the integrated communication system mayrefer to an end communication node of the core network that exchangespackets (e.g., control information, data) with the base station, and theMME (or, AMF) of the integrated communication system may refer to acommunication node in the core network that performs control functionsfor a wireless access section (or, interface) of the terminal. Here,each of the backhaul link, the fronthaul link, the Xhaul link, the XDU,the XCU, the BBU block, the S-GW, the MME, the AMF, and the UPF may bereferred to as a different term according to a function (e.g., functionof the Xhaul network, function of the core network) of a communicationprotocol depending on a radio access technology (RAT).

FIG. 4 is a conceptual diagram illustrating a first embodiment of anintegrated communication system.

Referring to FIG. 4, the integrated communications system may include anaccess network, an Xhaul network, and a core network. The Xhaul networkmay be located between the access network and the core network, and maysupport communications between the access network and the core network.The communication nodes belonging to the integrated communication systemmay be configured to be the same as or similar to the communication node200 shown in FIG. 2. The access network may include a TRP 430, aterminal 440, and the like. The Xhaul network may include a plurality ofcommunication nodes 420-1, 420-2, and 420-3. The communication nodeconstituting the Xhaul network may be referred to as an ‘XDU’. In theXhaul network, the XDUs 420-1, 420-2, and 420-3 may be connected usingwireless Xhaul links and may be connected based on a multi-hop scheme.The core network may include an S-GW/MME 410-1 (or, UPF/AMF), a P-GW410-2, and the like. The S-GW/MME 410-1 may refer to a communicationnode including an S-GW and an MME, and the UPF/AMF may refer to acommunication node an UPF and an AMF. The BBU block 450 may be locatedin the S-GW/MME 410-1 and may be connected to the third XDU 420-3 via awired link.

The first XDU 420-1 of the Xhaul network may be connected to the TRP 430using a wired link. Alternatively, the first XDU 420-1 may be integratedinto the TRP 430. The second XDU 420-2 may be connected to each of thefirst XDU 420-1 and the third XDU 420-3 using a wireless link (e.g.,wireless Xhaul link), and the third XDU 420-3 may be connected to an endcommunication node (e.g., the S-GW/MME 410-1) of the core network usinga wired link. Among the plurality of XDUs 420-1, 420-2, and 420-3 of theXhaul network, an XDU connected to an end communication node of the corenetwork may be referred to as an ‘XDU aggregator’. That is, the thirdXDU 420-3 in the Xhaul network may be the XDU aggregator. The functionsof the XDU aggregator may be performed by the S-GW/MME 410-1 in the corenetwork.

The communications between the plurality of XDUs 420-1, 420-2 and 420-3may be performed using a communication protocol for the Xhaul link(hereinafter, ‘Xhaul protocol’), which is different from an accessprotocol (e.g., a communication protocol used for communications betweenthe terminal 440 and the TRP 430 (or, macro base station, small basestation)). Packets to which the Xhaul protocol is applied may betransmitted to each of the core network and the access network throughthe Xhaul link. Here, the packets may indicate control information,data, and the like.

The TRP 430 may provide communication services to the terminal 440 usingan access protocol (e.g., 4G communication protocol, 5G communicationprotocol), and may be connected to the first XDU 420-1 using a wiredlink. The TRP 430 may support a remote radio transmission and receptionfunction among all the functions according to the communicationprotocol, and the baseband processing function for the TRP 430 may beperformed in the BBU block 450. A link (e.g., “TRP 430-first XDU420-1-second XDU 420-2-third XDU 420-3-BBU block 450 (or, SGW/MME410-1)”) between the TRP 430 performing the remote radio transmissionand reception function and the BBU block 450 performing the basebandprocessing function may be referred to as a ‘fronthaul link’. Forexample, the fronthaul link may be configured differently depending onthe location of the BBU block 450 performing the baseband processingfunction.

FIG. 5 is a conceptual diagram illustrating a second embodiment of anintegrated communication system.

Referring to FIG. 5, the integrated communications system may include anaccess network, an Xhaul network, and a core network. The Xhaul networkmay be located between the access network and the core network, and maysupport communications between the access network and the core network.The communication nodes belonging to the integrated communication systemmay be configured to be the same as or similar to the communication node200 shown in FIG. 2. The access network may include a macro base station530, a small base station 540, a TRP 550, terminals 560-1, 560-2, and560-3, and the like. The Xhaul network may include a plurality ofcommunication nodes 520-1, 520-2, 520-3, 520-4, 520-5, and 520-6. Thecommunication node constituting the Xhaul network may be referred to asan ‘XDU’. In the Xhaul network, the XDUs 520-1, 520-2, 520-3, 520-4,520-5, and 520-6 may be connected using wireless Xhaul links and may beconnected based on a multi-hop scheme. A BBU block 570 may be located inone XDU among the plurality of XDUs 520-1, 520-2, 520-3, 520-4, 520-5,and 520-6. For example, the BBU block 570 may be located in the sixthXDU 520-6. The core network may include an S-GW/MME 510-1 (or, UPF/AMF),a P-GW 510-2, and the like. The S-GW/MME 510-1 may refer to acommunication node including an S-GW and an MME. The S-GW/MME 410-1 mayrefer to a communication node including an S-GW and an MME, and theUPF/AMF may refer to a communication node an UPF and an AMF.

The first XDU 520-1 of the Xhaul network may be connected to the macrobase station 530 using a wired link, or may be integrated into the macrobase station 530. The second XDU 520-2 of the Xhaul network may beconnected to the small base station 540 using a wired link, or may beintegrated into the small base station 540. The fifth XDU 520-5 of theXhaul network may be connected to the TRP 550 using a wired link, or maybe integrated into the TRP 550.

The fourth XDU 520-4 may be connected to an end communication node(e.g., the S-GW/MME 510-1) of the core network using a wired link. Amongthe plurality of XDUs 520-1, 520-2, 520-3, 520-4, 520-5, and 520-6, anXDU connected to an end communication node of the core network may bereferred to as an ‘XDU aggregator’. That is, the fourth XDU 520-4 may bethe XDU aggregator. The communications between the plurality of XDUs520-1, 520-2, 520-3, 520-4, 520-5, and 520-6 may be performed using theXhaul protocol. Packets (e.g., data, control information) to which theXhaul protocol is applied may be transmitted to each of the core networkand the access network via the Xhaul link.

The macro base station 530 may provide communication services to thefirst terminal 560-1 using an access protocol (e.g., 4G communicationprotocol, 5G communication protocol), and may be connected to the firstXDU 520-1 via a wired link. The macro base station 530 may be connectedto the core network via the Xhaul network, and a link of “macro basestation 530-first XDU 520-1-fourth XDU 520-4-S-GW/MME 510-1” may bereferred to as a ‘backhaul link’. The small base station 540 may providecommunication services to the second terminal 560-2 using an accessprotocol (e.g., 4G communication protocol, 5G communication protocol),and may be connected to the second XDU 520-2 using a wired link. Thesmall base station 540 may be connected to the core network via theXhaul network, and a link of “small base station 540-second XDU520-2-third XDU 520-3-fourth XDU 520-4-S-GW/MME 510-1” may be referredto as a ‘backhaul link’.

The TRP 550 may provide communication services to the third terminal560-3 using an access protocol (e.g., 4G communication protocol, 5Gcommunication protocol), and may be connected to the fifth XDU 520-5using a wired link. The TRP 550 may support a remote radio transmissionand reception function among all the functions according to thecommunication protocol, and the baseband processing function for the TRP550 may be performed in the BBU block 570. A link (e.g., a link of “TRP550-fifth XDU 520-5-BBU block 570 (or, sixth XDU 520-6)”) between theTRP 550 performing the remote radio transmission and reception functionand the BBU block 570 performing the baseband processing function may bereferred to as a ‘fronthaul link’, and a link (e.g., a link of “BBUblock 570 (or, sixth XDU 520-6)-fourth XDU 520-4-S-GW/MME 510-1”)between the BBU block 570 and the S-GW/MME 510-1 may be referred to as a‘backhaul link’. For example, the fronthaul link may be configureddifferently depending on the location of the BBU block 570 performingthe baseband processing function.

Meanwhile, in the integrated communication system, a path configuration(or, path mapping, connection configuration, or connection mapping)between the XDUs may be completed for transmission and reception ofpackets (e.g., data, control information) between the XDUs. Here, thepath configuration may be referred to as a ‘path set’, a ‘pathestablishment’, a ‘path mapping’, a ‘route set’, a ‘routeestablishment’, a ‘route mapping’, a ‘route configuration procedure’, orthe like. The connection configuration may be referred to as a‘connection set’, a ‘connection establishment’, or the like.

In an upper layer of the Xhaul protocol (e.g., an upper layer above thePHY layer), a transmission control protocol (TCP)/Internet protocol(IP), an Ethernet, a user datagram protocol (UDP)/real time protocol(RTP), a multiprotocol label switching (MPLS) protocol, a general packetradio service (GPRS) tunneling protocol (GTP), or a L2 layer switching(e.g., a method of applying labeling, a method of using a separateheader field, etc.), or the like may be used.

The completed state of the path configuration among the XDUs may referto a state in which packets (e.g., data or control information) can betransmitted and received in the path among the corresponding XDUs (e.g.,a source XDU, one or more waypoint XDUs, a destination XDU, and thelike) by using unique identifiers (e.g., IP address, label, informationincluded in the header field, information included in controlinformation, etc.).

The path configuration among the XDUs may be performed by the XDU or theXCU. For example, in the XDU or the XCU, a block (hereinafter referredto as ‘PM function block’ or ‘RM function block’) supporting a pathmanagement (PM) function or a routing management (RM) function maycontrol a path configuration procedure a path release procedure, a pathactivation procedure, a path inactivation procedure, and the like.

The XCU may perform control management functions of the Xhaul network.For example, the XCU may manage a topology of Xhaul network, managepaths in the Xhaul network, and control XDUs constituting the Xhaulnetwork. The XCU may be directly connected to an XDU aggregator or aspecific XDU. Also, the XCU may perform an information exchangeoperation and a control operation with the core network. The XCU mayperform internal signaling operations and control operations with thefunction blocks in the communication nodes (e.g., XCU, XDU) constitutingthe Xhaul network in order to control the Xhaul network. The XCU mayperform the PM function for path control and management in the Xhaulnetwork, perform a mobility management (MM) function for mobilitycontrol and management in the Xhaul network, and perform a load control(LC) function for load control and management for Xhaul links in theXhaul network.

The PM function block may perform control and management functions forpaths created or changed according to the control messages received fromthe XDU and the operations of the function blocks in the XCU. The PMfunction block may identify whether a path among the XDUs is establishedin the Xhaul network, and may manage path configuration information, arouting table, a flow table, and the like based on the identifiedresult.

The MM function block may perform control procedures related to themobility of the XDU, and may change the path configuration information,the routing table, the flow table, and the like in conjunction with thePM function block in order to change the path according to the mobilityof the XDU. Also, the MM function block may perform control andmanagement functions for measurement and reporting on the XDU in orderto control the mobility of the XDU.

The XCU may create and manage XDU contexts for the respective XDUs forpath, mobility and load control and management in the Xhaul network. TheXDU context may be created when the corresponding XDU is attached (e.g.,registered) to the integrated communication system (e.g., Xhaulnetwork), and may be deleted when the corresponding XUD is detached(e.g., registration-released) from the integrated communication system(e.g., Xhaul network).

In the Xhaul network, the mobility support function may be used for amobile device having XDU functionality. Here, the mobile device may bean unmanned aerial vehicle, a drone, an autonomous vehicle, a vehiclerunning on a navigation function, or the like. In the Xhaul network, themobility support function may provide service continuity for the mobileXDUs. In the Xhaul network, the mobility support function may be usedfor a beam change between XDUs (e.g., sectors constituting XDUs) havingdifferent service areas (e.g., coverage), or used for an intra-frequencyor inter-frequency XDU change. Since the Xhaul link requires highertransmission reliability than the access link (e.g., channel) for theterminal, mobility functions without service interruption or packet lossshould be supported in the Xhaul network.

FIG. 6 is a conceptual illustrating a first embodiment of abeamforming-based communication method in a communication system.

Referring to FIG. 6, a communication system may include base stations611, 612 and 613, terminals 621 and 622, and the like, and thecommunication nodes (e.g., base stations, terminals) may performcommunications based on a beamforming scheme. For example, each of thebase stations 611, 612 and 613 may communicate using a plurality ofbeams (e.g., beams #1 to #4), and each of the terminals 621 and 622 mayalso communicate using the plurality of beams (e.g., beams #1 to #4).

An operational state of the first terminal 621 may be a state in which aconnection establishment with the first base station 611 is completed.For example, the operational state of the first terminal 621 may be aradio resource control (RRC) connected (RRC_CONNECTED) state or an RRCinactive (RRC_INACTIVE) state. Alternatively, the first terminal 621 mayoperate in an RRC idle (RRC_IDLE) state within a service area of thefirst base station 611. An operational state of the second terminal 622may be a state in which a connection establishment with the second basestation 612 or the third base station 613 is completed. For example, theoperational state of the second terminal 622 may be an RRC_CONNECTEDstate or an RRC_INACTIVE state. Alternatively, the second terminal 622may operate in an RRC_IDLE state within a service area of the secondbase station 612 or the third base station 613.

The base stations 611, 612 and 613 may support mobility functions andthus the mobility of the terminals 621 and 622 may be ensured betweenthe base stations 611, 612 and 613. Signals received from the terminals621 and 622 may be used by the base stations 611, 612, and 613 to selectan optimal beam.

In a communication system supporting a high frequency band, a function(e.g., a mobility support function and a radio resource managementfunction) of changing a configured beam of the first terminal 621 at thefirst base station 611 may be considered, and a function (e.g., amobility support function and a radio resource management function) ofchanging a configured beam of the second terminal 622 between the secondbase station 612 and the third base station 613 may be considered. Here,the configured beam may be a serving beam.

For example, in the case that the beam #3 of the first base station 611is paired with the beam #2 of the first terminal 621, the beam #3 of thefirst base station 611 paired with the beam #2 of the first terminal 621may be changed to another beam (e.g., the beam #2 or #4 of the firstbase station 611) according to a quality change of a radio channelbetween the first base station 611 and the first terminal 621.Alternatively, the beam #2 of the first terminal 621 paired with thebeam #3 of the first base station 611 may be changed to another beam(e.g., the beam #1, #3, or #4 of the first terminal 621).

Meanwhile, in the case that the beam #4 of the second base station 612is paired with the beam #3 of the second terminal 622, a handoverprocedure for changing the configured beam of the second terminal 622may be performed between the second base station 612 and the third basestation 613 according to a quality change of a radio channel between thesecond base station 612 and the second terminal 622.

In order to perform the mobility support function and the radio resourcemanagement function (e.g., handover procedure), the base stations 611,612 and 613 may transmit synchronization signals or reference signals,and the terminals 621 and 622 may perform search and monitoring on thebase stations 611, 612 and 613 (e.g., beams of the base stations 611,612, and 613) using the synchronization signals or the reference signalsreceived from the base stations 611, 612, and 613. Here, each of thesynchronization signals may be a primary synchronization signal (PSS), asecondary synchronization signal (SSS), a synchronizationsignal/physical broadcast channel (SS/PBCH) block, or the like. Each ofthe reference signals may be a cell-specific reference signal (CRS), ademodulation reference signal (DMRS), a channel stateinformation-reference signal (CSI-RS), a tracking reference signal(TRS), or the like.

The communication system may support numerologies defined in Table 1below and the base stations 611, 612 and 613 may provide synchronizationsignals or reference signals according to a default numerology (e.g.,μ=0). Accordingly, the terminals 621 and 622 may assume that the defaultnumerology (e.g., μ=0) is used, and perform search and monitoring on thesynchronization signals and reference signals according to the defaultnumerology (e.g., μ=0).

TABLE 1 μ Subcarrier spacing (Δf = 2^(μ) · 15 kHz) Type of Cyclic Prefix(CP) 0 15 kHz Normal 1 30 kHz Normal 2 60 kHz Normal or Extended 3 120kHz Normal 4 240 kHz Normal 5 480 kHz Normal

Here, the default numerology may be a frame format applied to a radioresource in which a user equipment (UE) common search space isconfigured, a frame format applied to a radio resource in which acontrol resource set (CORESET) of a NR system is configured, a frameformat applied to a radio resource through which a burst of SS/PBCHblocks (e.g., SS burst) are transmitted, or the like.

Meanwhile, the terminals 621 and 622 connected to the base stations 611,612 and 613 may transmit uplink-dedicated reference signals (e.g.,sounding reference signal (SRS)) in uplink resources assigned by thebase stations 611, 612 and 623. Alternatively, the terminals 621 and 622connected to the base stations 611, 612 and 613 may receivedownlink-dedicated reference signals configured by the base stations611, 612 and 623.

For example, in order for the first terminal 621 located in the servicearea of the first base station 611 to search for the first base station611, and perform a synchronization acquisition operation, a beamconfiguration operation, a radio link monitoring operation, or the like,the first base station 611 may transmit synchronization signals andreference signals. The first terminal 621 connected to the first basestation 611 may receive physical layer (e.g., PHY layer) radio resourceconfiguration information for connection establishment and radioresource management from the first base station 611 (e.g., serving basestation).

Here, the PHY layer radio resource configuration information may beparameters in an RRC message. For example, in the LTE system, theparameters included in the RRC message may be PhysicalConfigDedicated,PUCCH-Config, RACH-ConfigCommon, RACH-ConfigDedicated,RadioResourceConfigCommon, RadioResourceConfigDedicated, and the like.

The PHY layer radio resource configuration information may include achannel/signal/resource configuration cycle (e.g., allocation cycle)according to a frame format of the base station (e.g., a numerologysupported by the base station), time-frequency position information of aradio resource for transmission and reception of a channel or signal, atransmission time (e.g., allocation time) of the radio resource fortransmission and reception of the channel or signal, and the like. Here,the frame format may indicate a subframe having a length according tothe numerology (e.g., subcarrier spacing).

For example, in a radio frame (e.g., a radio frame having the length of10 milliseconds (ms)), the numbers of symbols constituting a subframe, aslot, and a mini-slot may be different. For example, the length of eachsubframe may be 1 ms, and each slot may include 14 symbols. Meanwhile,each mini-slot may have 2, 4, or 7 symbols.

-   -   Transmission frequency information and frame format information        of a base station        -   Transmission frequency information: all transmission            carriers (e.g., transmission frequency for a unit cell) or            bandwidth parts (BWPs) supported by the base station, a            transmission time reference or a time difference (e.g., a            transmission cycle or an offset parameter indicating a            transmission time reference (or, time difference) between            the synchronization signals) between the transmission            frequencies supported by the base station, and the like.        -   Frame format information: configuration parameters for the            subframe, slot, and mini-slot configured according to a            subcarrier spacing.    -   Configuration information of downlink reference signals (e.g.,        CSI-RS, common-RS, and the like)        -   Transmission cycle, transmission positions, code sequence,            masking sequence, scrambling sequence, etc. of reference            signals (e.g., common-RS) commonly applied to a coverage of            the base station (or, beam), and the like.    -   Configuration information of uplink reference signals and        control signals        -   Configuration information of SRS, configuration information            of reference signals for uplink beam sweeping, configuration            information of reference signals for uplink beam monitoring,            configuration information of radio resources (or, preamble)            for grant-free uplink transmissions, and the like.    -   Configuration information of physical downlink control channel        (PDCCH)        -   Configuration information of reference signals for            demodulation of PDCCH, configuration information of            beam-common reference signals (e.g., reference signals that            all terminals belonging to a beam coverage are able to            receive), configuration information of reference signals for            beam sweeping, configuration information of reference            signals for channel estimation, and the like.    -   Configuration information of physical uplink control channel        (PUCCH)    -   Configuration information of resources for transmitting and        receiving a scheduling request (SR).    -   Configuration information of resources for transmitting and        receiving hybrid automatic repeat request (HARQ) responses        (e.g., acknowledgement (ACK) or negative ACK (HACK)).    -   The number of antenna ports, information on an arrangement of        antennas, beam configuration or beam index mapping information        for beamforming.    -   Configuration information of downlink and uplink signals and        resources for beam sweeping.    -   Configuration information of a beam configuration operation, a        beam recovery operation, a beam reconfiguration operation, a        radio link re-establishment operation, a beam switching        operation within a same base station, triggering signals for a        handover operation for beam switching between base stations,        timers for controlling the above-described operations, and the        like.

The configuration information and parameters described above may beconfigured to be applied to the frame formats according to thenumerologies defined in Table 1.

In the following embodiments, “Resource-Config information” may be acontrol message (e.g., RRC message) including one or more pieces of theconfiguration information (e.g., parameters) among the above-describedPHY layer radio resource configuration information. The “Resource-Configinformation” may be commonly applied to the entire coverage (e.g., beamcoverage) of the base station. Alternatively, the “Resource-Configinformation” may be configuration information dedicated to a specificterminal or a specific terminal group. The configuration informationincluded in the “Resource-Config information” may be configured as asingle control message. Alternatively, the configuration informationincluded in the “Resource-Config information” may be configured as aplurality of control messages according to attributes of thecorresponding configuration information. Beam index information mayindicate at least one of a transmission beam index and a reception beamindex.

Thus, a communication service for the first terminal 621 connected tothe first base station 611 may be provided through the configured beamof the first base station 611. In the case that the beam #3 of the firstbase station 611 is paired with the beam #2 of the first terminal 621,the first terminal 621 may use at least one of the synchronizationsignals transmitted from the first base station 611 and the referencesignals transmitted through the beam #3 of the first base station 611 tosearch for or monitor a downlink radio channel (e.g., downlink radiolink). The monitoring operation on the downlink radio channel (e.g.,downlink radio link) may refer to a radio link monitoring (RLM), and thefirst terminal 621 may detect a problem of the radio link by performingthe RLM.

Here, the detection of the problem of the radio link may mean that thesynchronization of the PHY layer is not maintained in the correspondingradio link. For example, the first terminal 621 may determine that aradio link problem has occurred when the synchronization between thefirst base station 611 and the first terminal 621 is not maintained fora preset time. When the radio link problem is detected, the firstterminal 621 may perform a recovery operation on the corresponding radiolink. When the recovery operation on the radio link fails, the firstterminal 621 may declare a radio link failure (RLF) and perform a radiolink re-establishment operation.

The radio link problem detection operation, the radio link recoveryoperation, the RLF declaration operation, the radio linkre-establishment operation, and the like may be performed by layersbelonging to the communication node. The layers belonging to thecommunication node may include a layer 1 (e.g., PHY layer), a layer 2(e.g., a medium access control (MAC) layer, a radio link control (RLC)layer, a packet data convergence protocol (PDCP) layer), a layer 3(e.g., an RRC layer), and the like.

The PHY layer of the terminal may monitor the radio link by receiving atleast one of the synchronization signals and the reference signals.Here, each of the reference signals may be a common reference signal ofthe base station, a beam common reference signal, a dedicated referencesignal assigned to a terminal or a specific terminal group, or the like.The common reference signal may be a reference signal that can bereceived by all the terminals located within the coverage of the basestation or within the coverage of the beam, and the terminal mayestimate the radio channel using the common reference signal. Thededicated reference signal may be a reference signal that can bereceived by a specific terminal (or a terminal belonging to a specificterminal group) located within the coverage of the base station or thecoverage of the beam, and the specific terminal (or, the terminalbelonging to the specific terminal group) may estimate the radio channelusing the dedicated reference signal.

Therefore, when the base station is changed or the configured beam ischanged, a procedure of changing the configuration information (e.g.,parameters) of the dedicated reference signal between the terminal andthe base station may be performed. The configuration information of thecommon reference signal may be transmitted through system information(e.g., physical broadcast channel (PBCH)), and in this case, theterminal may identify the configuration information of the commonreference signal included in the system information received from thebase station. In the handover procedure, the configuration informationof the common reference signal may be transmitted through a dedicatedcontrol message (e.g., RRC message), and in this case, the terminal mayidentify the configuration information of the common reference signalindicated by the dedicated control message received from the basestation.

In order to ensure service continuity, the base station may allocatemultiple beams to the terminal. Referring to FIG. 6, the first basestation 611 may allocate the beams #2 to #4 to the first terminal 621,and the second base station 612 may allocate the beams #3 to #4 to thesecond terminal 621. The state in which the beams are allocated mayrefer to a state in which a transmission beam of the base station and areception beam of the terminal are determined (e.g., a state in which abeam pairing is completed), and transmission and receptions operationsfor data and control information may be possible in the state in whichthe beams are determined. Alternatively, the operation of allocating thebeams may mean an operation of configuring beams so that the terminalcan perform a beam sweeping operation or a beam measurement and reportoperation.

The plurality of beams may be allocated in consideration of a movementspeed of the terminal, a movement direction of the terminal, a positionof the terminal, a quality of the radio link or channel, beam qualities,beam interferences, or the like. For example, when the movement speed ofthe first terminal 621 is less than or equal to a preset thresholdvalue, the first base station 611 may allocate the adjacent beams #2 to#3 to the first terminal 621. On the other hand, when the movement speedof the first terminal 621 exceeds the preset threshold value, the firstbase station 611 may allocate, to the first terminal 621, the beams #2and #4 spaced apart from each other.

In the case that the second terminal 622 moves from the coverage of thesecond base station 612 to the coverage of the third base station 613while a communication service for the second terminal 622 is providedthrough the beams #3 to #4 allocated by the second base station 612, anda cell (or, sector) to which the second base station 612 belongs isdifferent from a cell (or, sector) to which the third base station 613belongs, a handover procedure between the second base station 612 andthe third base station 613 may be performed.

When the handover procedure is performed, configuration information ofthe beams #1 to #2 of the third base station 613 may be transmitted fromthe third base station 613 to the second base station 612, and thesecond base station 612 may transmit to the second terminal 622 ahandover control message including the configuration information of thebeams #1 to #2 of the third base station 613. The configurationinformation may include beam index information (e.g., index oftransmission beam, and index of reception beam) configured according toresults of the beam sweeping operation or beam measurements,configuration information of the beams (e.g., transmission power, beamwidth, beam vertical angle, beam horizontal angle, etc.), transmissionand reception timing information of the beams (e.g., index or offset inunits of subframes, slots, mini-slots, or symbols), configurationinformation of reference signals transmitted through the beams (e.g.,sequence, index, etc.), and the like.

A control message including the above-described information required forbeam allocation may be transmitted among the second base station 612,the third base station 613, and the second terminal 622 in order toallocate a plurality of beams to the second terminal 622.

On the other hand, in the case that the second terminal 622 moves fromthe coverage of the second base station 612 to the coverage of the thirdbase station 613 while the communication service for the second terminal622 is provided through the beams #3 to #4 allocated by the second basestation 612, and the second base station 612 and the third base station613 belong to a same cell (or, sector), a procedure for changing atransmission communication node (e.g., base station) within the cell maybe performed.

In this case, the second base station 612 and the third base station 613may be communication nodes (e.g., RRH, RTP, etc.) to which a functionsplit is applied. For example, each of the second base station 612 andthe third base station 613 may support at least one of a PHY layerfunction, a MAC layer function, a RLC layer function, a PDCP layerfunction, and an adaptation layer. Here, the adaptation layer may be alayer higher than the PDCP layer, and may include a mapping functionbetween a quality of service (QoS) flow and a data radio bearer (DRB), amarking function of a QoS flow identifier for a downlink packet or anuplink packet, and the like.

When the base stations 612 and 613 belonging to the same cell includesome layers (e.g., layers 1 and 2), the procedure for changing thetransmission node from the second base station 612 to the third basestation 613 may be performed through exchanges of MAC messages (e.g.,MAC control element (CE), control protocol data unit (PDU), etc.)without exchanging the RRC messages.

The layer responsible for generation, transmission, and reception of thecontrol messages for changing the base stations may be determinedaccording to the layers included in the corresponding base stations. Forexample, when each of the second base station 612 and the third basestation 613 includes a PHY layer to a MAC layer (or a PHY layer to anRLC layer), the control message for changing the base station may begenerated, transmitted, and received at a layer higher than the MAClayer (or, RLC layer). In the procedure for changing the base stations,the MAC layer (or the MAC layer and the RLC layer) of each of the basestations 612 and 613 and the second terminal 622 may be newly configuredafter being reset.

On the other hand, when each of the second base station 612 and thethird base station 613 includes only a PHY layer, or when each of thesecond base station 612 and the third base station 613 supports onlysome of the functions of the MAC layer, the control messages forchanging the base stations may be generated, transmitted, and receivedat the MAC layer. In this case, in the procedure for changing the basestations, the MAC layer of each of the base stations 612 and 613 and thesecond terminal 622 may not be reset.

In the procedure for changing the base stations, identificationinformation of the base station may be transmitted to the terminalthrough an RRC message, a MAC layer control message (i.e., MAC controlmessage), or a PHY layer control channel (e.g., downlink controlinformation (DCI)). The identification information of the base stationmay be an identifier, configuration information of at least onereference signal, configuration information of at least one allocatedbeam, or the like. The configuration information of at least onereference signal may be at least one of resource allocation information,sequence information, and index information for the reference signalconfigured for each base station. Alternatively, the configurationinformation of at least one reference signal may be at least one ofresource allocation information, sequence information, and indexinformation for the reference signal configured for each specificterminal (or, specific terminal group).

The allocated beam may be a configured beam, a serving beam, or thelike. The configuration information of at least one allocated beam mayinclude at least one of a transmission power of the beam, a width of thebeam, a vertical angle of the beam, a horizontal angle of the beam,transmission and reception timing information of the beam (e.g., indexor offset in units of subframes, slots, mini-slots, or symbols),configuration information of reference signals transmitted through thebeams (e.g., sequence, index, etc.), and the like.

Accordingly, the terminal may obtain the identification information ofthe base station from the RRC message, the MAC control message, or thePHY layer control channel, and may identify a base station with whichthe terminal is to perform a beam sweeping operation, a radio accessoperation, a transmission and reception operation of control informationand data, and the like.

In the case that a plurality of beams are allocated, communicationsbetween the base station and the terminal may be performed using theplurality of allocated beams. In this case, the number of downlink beamsmay be the same as the number of uplink beams. Alternatively, the numberof downlink beams may be different from the number of uplink beams. Forexample, the number of downlink beams may be two or more, and the numberof uplink beams may be one. Alternatively, in the case that a pluralityof beams are allocated, the communications between the base station andthe terminal may be performed using one or more beams among theplurality of allocated beams, and the remaining beams not used for thecommunications may be configured as ‘reserved beams’ (e.g., candidatebeams). For example, the plurality of beams may be configured as aprimary beam, a secondary beam, or one or more reserved beams (e.g.,candidate beams).

For example, the primary beam may be used for transmitting and receivingdata and control information, and the secondary beam may be used fortransmitting and receiving data. The signaling of the controlinformation over the secondary beam may be restricted for each layer(e.g., layer 1, layer 2, or layer 3). Alternatively, the signaling ofthe control information over the secondary beam may be partiallyrestricted according to each function within the layer. Alternatively,the signaling of the control information over the secondary beam may berestricted depending on the type of the control messages. The controlmessages may be classified according to a discontinuous reception (DRX)or discontinuous transmission (DRX) operation, a retransmissionoperation, a connection configuration and management operation, ameasurement and report operation, a paging operation, an accessoperation, or the like.

Transmission and reception of data and control information over thereserved beam (e.g., candidate beam) may be restricted. The reservedbeam (e.g., candidate beam) may be used for the beam sweeping operationor the beam measurement and report operation. In this case, the terminalmay report the measurement result of the reserved beam to the basestation using the primary beam or the secondary beam. The measurementand report operation for the reserved beam may be performed based onpreset parameters. For example, the measurement and report operation forthe reserved beam may be performed periodically or aperiodicallyaccording to determination of the terminal or when a specific event isgenerated. Each of the measurement result on the reserved beam and theresult of the beam sweeping for the reserved beam may be transmittedthrough a PHY layer control channel (e.g., PUCCH) or a MAC controlmessage (e.g., MAC control PDU). Here, the result of the beam sweepingmay be a measurement result for one or more beams (or, beam group).

The base station may receive the beam measurement result or the beamsweeping result from the terminal, and may change properties (e.g.,primary beam, secondary beam, reserved beam, active beam, inactive beam,or the like) of the beams. A beam (e.g., primary beam or secondary beam)that is capable of transmitting and receiving at least one among dataand control information may be referred to as an active beam or aserving beam. A beam (e.g., reserved beam or candidate beam) that is notcapable of transmitting and receiving data and control information maybe referred to as an inactive beam or a neighbor beam.

A procedure for changing the beam property may be controlled in the MAClayer or the RRC layer. When the procedure for changing the beamproperty is performed in the MAC layer, the MAC layer may transmitinformation indicating that the beam property has been changed to anupper layer (e.g., the RRC layer). Also, the information indicating thatthe beam property has been changed may be transmitted from the basestation to the terminal through a MAC control message or a PHY layercontrol channel (e.g., PDCCH). When the PHY layer control channel isused, the information indicating that the beam property has been changedmay be included in a DCI, an uplink control information (UCI), or aseparate field (e.g., an indicator).

The terminal may transmit to the base station information requesting achange of the beam property based on the beam measurement result or thebeam sweeping result. The information requesting the change of the beamproperty may be transmitted through a PHY layer control channel, a MACcontrol message or an RRC message. Here, each of the PHY layer controlchannel, the MAC control message, and the RRC message may include one ormore pieces of the configuration information of at least one allocatedbeam described above.

According to the above-described procedure for changing the beamproperty, the beam property may be changed as follows.

-   -   active beam→inactive beam    -   inactive beam→active beam    -   primary beam→secondary beam    -   secondary beam→primary beam    -   primary beam→reserved beam (e.g., candidate beam)    -   reserved beam (e.g., candidate beam)→primary beam    -   secondary beam→reserved beam (e.g., candidate beam)    -   reserved beam (e.g., candidate beam)→secondary beam

The procedure for changing beam property may be performed in a MAC layeror an RRC layer. The procedure for changing beam property may beperformed through cooperation between the MAC layer and the RRC layerwhen necessary.

When a plurality of beams are allocated, a beam used for transmissionand reception of a PHY layer control channel may be configured among theplurality of beams. For example, the PHY layer control channel may beconfigured to be transmitted and received using a plurality of beams(e.g., primary beam and secondary beam). Alternatively, the PHY layercontrol channel may be configured to be transmitted and received using aprimary beam among the plurality of beams.

The PHY layer control channel may be a PDCCH or a PUCCH. The PHY layercontrol channel may be used for transmission of at least one ofscheduling information including resource allocation information (e.g.,resource element (RE) allocation information and modulation and codingscheme (MCS) information), a channel quality indicator (CQI), aprecoding matrix indicator (PMI), a HARQ response (e.g., ACK/NACK),resource request information (e.g., scheduling request (SR)), a beamsweeping result for supporting beamforming (e.g., beam indexes), and ameasurement result on active beams and inactive beams.

In the case that a plurality of beams are allocated, configurationinformation of the plurality of beams (e.g., beam indexes, an intervalbetween the allocated beams, information indicating whether contiguousbeams are allocated, or the like) may be transmitted and receivedthrough a signaling procedure between the base station and the terminal.

The signaling procedure for transmitting and receiving the configurationinformation of the plurality of beams may be performed differentlyaccording to mobility information (e.g., movement speed, movementdirection, position, etc.) of the terminal and quality information ofthe radio channel. The mobility information of the terminal and thequality information of the radio channel may be reported from theterminal to the base station. Alternatively, the mobility information ofthe terminal and the quality information of the radio channel may beacquired by the base station without the reporting of the terminal. Thequality information of the radio channel may include at least one of achannel state indicator (CSI), a received signal strength indicator(RSSI), a reference signal received power (RSRP), and a reference signalreceived quality (RSRQ).

In the above-described embodiments, the radio resource allocationinformation may include a frequency parameter indicating a radioresource allocated in the frequency axis and a time parameter indicatinga radio resource allocated in the time axis. The frequency parameter mayindicate at least one of a center frequency, a system bandwidth, abandwidth part, and a subcarrier. The time parameter may indicate atleast one of a radio frame, a subframe, a transmission time interval(TTI), a slot, a mini-slot, a symbol, transmission time information(e.g., cycle, duration, window), and reception time information (e.g.,cycle, duration, window).

Also, the radio resource allocation information may include a hoppingpattern of radio resources, configuration information of beamforming(e.g., transmission power, beam width, beam vertical angle, beamhorizontal angle, beam index, etc.), a code sequence (e.g., bit string,signal string), and the like. The type of the radio resource (e.g., thetype of the PHY layer channel or the type of the transport channel) mayvary according to the type (e.g., attribute) of control information, thetype of data, a transmission direction (e.g., uplink or downlink), acommunication scheme (e.g., sidelink communication), and the like.

FIG. 7 is a timing diagram illustrating a first embodiment of a beammanagement procedure in a communication system.

Referring to FIG. 7, a communication system may include base stations(e.g., the base stations 611, 612 and 613 shown in FIG. 6), terminals(e.g., terminals 621 and 622 shown in FIG. 6), and the like. Thecommunications between the base station and the terminal may beperformed based on a beamforming scheme. In the following embodiments, abeam monitoring operation may be performed by the base station or theterminal. For example, in the beam monitoring operation, the basestation or the terminal may measure a received signal quality for aplurality of beams (e.g., a plurality of beams including a servingbeam), and identify the plurality of beams based on results of themeasurement.

Also, the beam monitoring operation may be performed usingsynchronization signals or reference signals configured in accordancewith the default numerology. Alternatively, the beam monitoringoperation may be performed using synchronization signals or referencesignals configured according to a different numerology other than thedefault numerology. In this case, the base station may notify theterminal of the numerology (e.g., defined in Table 1) for the beammonitoring operation.

A beam or radio link management operation may include a beam problemdetection (BPD) step (e.g., a beam monitoring step) S702, a beamrecovery (BR) step S703, a beam reconfiguration step (e.g., a beamre-sweeping step) S704, and a radio link re-establishment step S705.Alternatively, the beam recovery step and the beam reconfiguration stepmay be configured as a single step. In this case, the beam or radio linkmanagement operation may include a beam problem detection step, a beamrecovery and reconfiguration step, and a radio link re-establishmentstep. Each of the steps constituting the beam or radio link managementoperation may be controlled by the MAC layer or the RRC layer.

The communications between the base station and the terminal may beperformed using one or more beams (e.g., beam #1, beam #2, . . . , beam#K). Here, K may be a positive integer. In a general operation stepS701, a synchronization configuration and management operation for thebeam configured between the base station and the terminal may beperformed. For example, the PHY layer of the terminal may determinewhether the synchronization of the PHY layer is maintained or not bymonitoring at least one of the synchronization signal and the referencesignal from the base station, and transmit a result of the determinationto an upper layer (e.g., MAC layer, RRC layer, or the like) of theterminal.

In the case that the synchronization with the base station is maintainedduring a monitoring period, the PHY layer of the terminal may transmitan in-synch indicator (hereinafter referred to as ‘IS_Ind’) indicatingthat the synchronization is maintained to the upper layer of theterminal. On the other hand, in the case that the synchronization withthe base station is not maintained during the monitoring period, the PHYlayer of the terminal may transmit an out-of-synch indicator(hereinafter referred to as ‘OoS_Ind’) indicating that thesynchronization is not maintained to the upper layer of the terminal.

Upon receiving the IS_Ind or the OoS_Ind is received from the PHY layerof the terminal, the upper layer (e.g., MAC layer, RRC layer) of theterminal may count the number of consecutively received IS_Inds orOoS_Inds, and may determine whether a downlink synchronization ismaintained or not based on the number of the received IS_Inds or QoSInds. Alternatively, the terminal may determine whether a downlinksynchronization is maintained or not based on a timer.

For example, if the IS_Ind is not received within a predetermined timefrom the reception of the OoS_Ind, the upper layer of the terminal maydetermine that the downlink synchronization is not maintained. In thecase that it is determined that the downlink synchronization is notmaintained based on the IS_Ind or the OoS_Ind, the terminal maydetermine that a beam problem is detected (S702). Alternatively, in thebeam problem detection step S702, the beam problem may be detected basedon a quality of a downlink signal (e.g., RSRP, RSRQ, etc.) or an errorrate of a downlink channel (e.g., bit error rate (BER), block error rate(BLER), etc.).

In the case that the quality of the downlink signal is used to detectthe beam problem, a reference value for the quality of the downlinksignal may be preconfigured, and when the quality of the downlink signalmeasured in the monitoring period is less than the reference value, itmay be determined that the beam problem is detected. Alternatively, inthe case that the error rate of the downlink channel (e.g., PDCCH,physical downlink shared channel (PDSCH), etc.) is used to the beamproblem, a reference value for the error rate of the downlink channelmay be preconfigured, and when the error rate of the downlink channelmeasured in the monitoring period is not less than the reference value,it may be determined that the beam problem is detected. That is, theerror rate of the downlink channel may be measured based on whetherreception of PDCCH or PDSCH is successful in the monitoring period.Here, the reference value used for detecting the beam problem may besignaled from the base station to the terminal.

In particular, the error rate of the PDCCH may be measured based on acyclic redundancy check (CRC) result for the PDCCH of the serving beam,a reception error rate of information mapped to a predetermined regionin a radio resource allocated for the PDCCH, a reception error rate of aspecific field (e.g., a specific parameter) constituting the PDCCH, orthe like. Alternatively, an error rate of an UE-common search space, anerror rate of an UE-specific search space, or an error rate of theUE-common search space and the UE-specific search space may be used asthe error rate of the PDCCH. Alternatively, an error rate of the CORESETmay be used as the error rate of the PDCCH.

Accordingly, the PHY layer of the terminal may transmit informationindicating a success or a failure of reception of the PDCCH or the errorrate of the PDCCH to the upper layer of the terminal for each receptioninterval (e.g., monitoring occasion) of the PDCCH. Upon receiving theinformation indicating the success or failure of reception of the PDCCHor the error rate of the PDCCH from the PHY layer of the terminal, theupper layer of the terminal may declare a beam problem detection (or,beam failure) based on the received information or error rate. In thiscase, the upper layer of the terminal may trigger the beam recovery stepS703 or the like.

Alternatively, when an uplink transmission is unsuccessful, the terminalmay declare that a beam problem is detected. If the number of times thatACKs for uplink transmissions (e.g., grant-free uplink transmissions, SRtransmissions, etc.) are not received is equal to or greater than apredetermined number, the terminal may declare a beam problem detection.Also, when a message directing adjustment of transmission timing of anuplink physical channel is not received from the base station before apreset timer expires, the terminal may declare a beam problem detection.

Alternatively, the base station may perform the beam monitoringoperation based on uplink reference signals, and may declare a beamproblem detection when a result of performing the beam monitoringoperation conforms to a beam problem detection condition. When the beamproblem is detected, the base station may transmit informationindicating that the beam problem is detected, information instructing toperform a beam recovery operation or a beam sweeping operation, orinformation instructing to perform uplink transmission using anotherbeam through a PDCCH, a paging channel, or a downlink channel (e.g., amulticast channel, a beam common channel, a base station common channel)that a plurality of terminals can receive. In this case, the basestation may transmit, to the terminal, an identifier of the terminal, anindex of a beam in which the beam problem is detected, indexes ofdownlink and uplink beams to be used by the terminal, and the like.

The above-described conditions used to detect the beam problem may beused to determine the success or failure of beam recovery afterdetection of the beam problem. When a plurality of beams are configured,the operation of detecting the beam problem in the beam problemdetection step S702 may be performed on a beam-by-beam basis. When thebeam problem is detected, the PHY layer, MAC layer or RRC layer of theterminal may trigger the beam recovery step S703 and the beamreconfiguration step S704, respectively.

The MAC layer may control a beam problem detection operation (i.e., thebeam problem detection step S702), a beam recovery operation (i.e., thebeam recovery step S703), and a beam reconfiguration operation (i.e.,the beam reconfiguration step S704) for the configured beam (e.g.,serving beam). Alternatively, some operations of the beam problemdetection operation, the beam recovery operation, and the beamreconfiguration operation may be controlled by the MAC layer.

For example, the PHY layer of the terminal may transmit the IS_Ind orthe OoS_Ind to the MAC layer of the terminal. In the case that thenumber of consecutively received OoS_Inds is equal to or greater than apredetermined value N or the IS_Ind is not received until apredetermined timer (e.g., timer for beam problem detection (T_(BPD)))expires after reception of the OoS_Ind, the MAC layer of the terminalmay determine that a PHY layer problem (e.g., beam problem) hasoccurred. Here, N may be a positive integer and the timer T_(BPD) may bestarted when the OoS_Ind is received after the reception of the IS_Indand may be reset when the IS_Ind is received after the reception of theOoS_Ind.

In the case that the number of consecutively received OoS_Inds is equalto or greater than N, the IS_Ind is not received until the expiration ofthe TBPD, or a beam problem is detected according to other reasons, theterminal may perform the beam recovery step S703 (or, the beam recoveryand reconfiguration step). In the beam recovery step S703 (or the beamrecovery and reconfiguration step), the PHY layer or MAC layer of theterminal may start a timer for beam recovery (T_(BR)), and transmitinformation indicating that the beam recovery step S703 (or, the beamrecovery and reconfiguration step) has been started to the upper layer(e.g., RRC layer) of the terminal. Also, the terminal may transmit tothe base station a PHY layer control channel, a MAC control message oran RRC message indicating that the beam recovery step S703 (or the beamrecovery and reconfiguration step) has been started.

In the case that the IS_Ind is received until expiration of the T_(BR)or it is recognized that the beam recovery is completed by anothermethod, the PHY layer or MAC layer of the terminal may transmitinformation on the recovered beam (e.g., beam index, measurement resultof the beam, etc.) to the upper layer (e.g., RRC layer) of the terminal.In this case, the terminal may perform communications with the basestation using the recovered beam.

Also, the terminal may transmit a PHY layer control channel, a MACcontrol message, or an RRC message indicating the completion of the beamrecovery to the base station. In this case, information indicating thatthe recovered beam is the same as the beam in which the beam problem isdetected may also be transmitted to the base station via the PHY layercontrol channel, MAC control message or RRC message.

On the other hand, in the case that the IS_Ind is not received until theexpiration of the T_(BR), or the beam failure is recognized by anothermethod, the terminal may perform the beam reconfiguration step S704. Inthe beam reconfiguration step S704, the terminal may perform the beamreconfiguration operation by using the configuration information ofneighbor beams obtained in the connection configuration procedurebetween the terminal and the base station, obtained from systeminformation, or obtained through the beam sweeping operation.

In the case that a beam pairing procedure with another beam among theplurality of beams of the same base station, which is other than thebeam in which the beam problem is detected in the step S702, iscompleted until expiration of a timer for beam pairing (T_(BP)), it maybe determined that the beam reconfiguration operation has beensuccessfully completed. The beam reconfiguration step S704 may beperformed for each of scenarios #1 and #2 below.

-   -   Scenario #1: a case in which the terminal has Resource-Config        information for the newly-configured beam    -   Scenario #2: a case in which the terminal does not have        Resource-Config information for the newly-configured beam

In the case that the beam reconfiguration operation has beensuccessfully completed in the scenario #1, the PHY layer or the MAClayer of the terminal may transmit the configuration information of thereconfigured beam (e.g., beam index, etc.) and information indicatingthat the beam reconfiguration operation has been successfully completedto the upper layer (e.g., RRC layer) of the terminal. The terminal mayperform communications with the base station using the reconfigured beamwithout updating (or reconfiguring) the Resource-Config information.Also, the terminal may transmit a PHY layer control channel, a MACcontrol message, or an RRC message indicating that the beamreconfiguration operation has been successfully completed to the basestation. In this case, the configuration information of the reconfiguredbeam may also be transmitted to the base station through the PHY layercontrol channel, the MAC control message, or the RRC message.

In the case that the beam reconfiguration operation has beensuccessfully completed in the scenario #2, the PHY layer or the MAClayer of the terminal may transmit the configuration information of thereconfigured beam (e.g., beam index, etc.) and information indicatingthat the beam reconfiguration operation has been successfully completedto the upper layer (e.g., RRC layer) of the terminal.

When it is identified that the beam reconfiguration operation has beensuccessfully completed, the RRC layer of the terminal may transmit anRRC message requesting configuration of a resource for the reconfiguredbeam to the base station. Alternatively, a MAC control messagerequesting configuration of a resource for the reconfigured beam may betransmitted to the base station instead of the RRC message. Uponreceiving the information indicating that the beam reconfigurationoperation has been successfully completed and the information requestingresource configuration for the reconfigured beam from the terminal, thebase station may generate Resource-Config information for thereconfigured beam, and transmit a message including the generatedResource-Config information to the terminal.

Also, when it is reported to the base station that the beamreconfiguration operation has been successfully completed, the terminalmay report a measurement result for the plurality of beams of the basestation to the base station. In this case, the base station may selectanother beam other than the beam reconfigured by the terminal based onthe measurement result received from the terminal, and transmit amessage including information instructing to perform a reconfigurationoperation with the selected beam or configuration information of theselected beam.

However, in the case that the beam reconfiguration operation is notcompleted until the expiration of the T_(BP), the terminal may determinethat an RLF has occurred. In this case, the terminal may perform theradio link re-establishment step S705. In the case that the beamdetection operations, the beam recovery operations, and the beamreconfiguration operations have been performed for the plurality ofbeams, or the T_(BP)s for all the beams have been expired, the terminalmay determine that an RLF has occurred.

Alternatively, in the case that a plurality of beams are configured(e.g., when a plurality of serving beams are configured), the terminalmay determine that an RLF has occurred when the beam reconfigurationoperation for the primary beam among the plurality of beams fails. Forexample, when the primary beam is the beam #1 in FIG. 7, the terminalmay determine that an RLF has occurred at the end of the beamreconfiguration step S704-1 when the beam reconfiguration operation forthe beam #1 has failed. In this case, the beam reconfigurationoperations for the remaining beams (e.g., beam #2, . . . , beam #K) maybe terminated. That is, the timers for the beam reconfigurationoperations for the remaining beams (e.g., beam #2, . . . , beam #K) maybe stopped.

However, when necessary, after the beam reconfiguration steps (S704-1,S704-2, . . . S704-K) for all the beams (e.g., beam #1, beam #2, . . . ,beam #K), the terminal may determine whether or not the RLF hasoccurred. In this case, the starting points of the radio linkre-establishment steps (S705-1, S705-2, . . . S705-K) for all the beams(e.g., beam #1, beam #2, . . . , beam #K) may be aligned to the timewhen it is determined that the RLF has occurred. When the beamreconfiguration operation has not been successfully completed until theexpiration of the T_(BP) or it is determined by another method that theRLF has occurred, the terminal may perform the radio linkre-establishment operation by searching for beams of the base station(e.g., the same base station or another base station) until expirationof a timer for re-establishment (e.g., T_(Re-est)).

When the radio link re-establishment operation has been successfullycompleted, the base station may generate a message including theResource-Config information (e.g., a message for establishing aconnection) and transmit the generated message to the terminal. Theterminal may receive the message including the Resource-Configinformation from the base station, and may configure the correspondingparameters based on the Resource-Config information included in themessage.

When the radio link re-establishment operation with the base station hasnot been completed until the expiration of T_(Re-est), the operationalstate of the terminal may transition from the RRC_CONNECTED state to theRRC_INACTIVE state or the RRC_IDLE state. For example, when theT_(Re-est)s for all the beams (e.g., beam #1, beam #2, . . . , beam #K)are terminated, the operational state of the terminal may transitionfrom the RRC_CONNECTED state to the RRC_INACTIVE state or the RRC_IDLEstate.

In the case that a plurality of beams (e.g., beam #1, beam #2, . . . ,and beam #K shown in FIG. 7) are configured between the base station andthe terminal and the beam #1 in FIG. 7 is the primary beam, when thebeam recovery operation on the primary beam (e.g., the beam #1) hasfailed, irrespective of the beam recovery operations for the other beams(e.g., beam #2, . . . , beam #K), the terminal may declare a beamfailure at the end of the beam recovery step S703-1, and perform thebeam reconfiguration operation after the declaration of the beamfailure.

Also, in the case that a plurality of beams (e.g., beam #1, beam #2, . .. , and beam #K shown in FIG. 7) are configured between the base stationand the terminal and the beam #1 in FIG. 7 is the primary beam, when thebeam reconfiguration operation on the primary beam (e.g., the beam #1)has failed, irrespective of the beam reconfiguration operations for theother beams (e.g., beam #2, . . . , beam #K), the terminal may declare abeam failure at the end of the beam reconfiguration step S704-1, andperform the radio link re-establishment operation after the declarationof the beam failure.

The beam reconfiguration step S704 may be performed after the beamrecovery step S703. That is, the beam recovery step S703 and the beamreconfiguration step S704 may be performed consecutively in the timeaxis. Alternatively, the beam recovery step S703 and the beamreconfiguration step S704 may be performed in parallel. For example,when a received signal quality (e.g., RSSI, RSRP, RSRQ, etc.) measuredin the beam recovery step S703 is equal to or less than a predeterminedreference value, the beam reconfiguration step S704 may be performedeven before the expiration of the T_(BR). A condition (e.g., a referencevalue for the beam reception signal or a separate timer for triggeringthe beam reconfiguration step S704 (e.g., T_(early_BP)) before the endpoint of the beam recovery step S703 may be configured. Here, thereference value and a setting value for the T_(early_BP) may betransmitted to the terminal through system information or a controlmessage (e.g., control message including the Resource-Configinformation).

Also, the radio link re-establishment step S705 may be performed afterthe beam reconfiguration step S704. That is, the beam reconfigurationstep S704 and the radio link re-establishment step S705 may be performedconsecutively in the time axis. Alternatively, the beam reconfigurationstep S704 and the radio link re-establishment step S705 may be performedin parallel. For example, when a received signal quality (e.g., RSSI,RSRP, RSRQ, etc.) measured in the beam reconfiguration step S704 isequal to or less than a predetermined reference value, the radio linkre-establishment step S705 (or, a preparation operation for the radiolink re-establishment) may be performed even before the expiration ofthe T_(BP).

A condition (e.g., a reference value for the beam reception signal or aseparate timer for triggering the radio link re-establishment step S705(e.g., T_(early_ReEST))) before the end point of the beamreconfiguration step S704 may be configured. Here, the reference valueand a setting value for the T_(early_ReEST) may be transmitted to theterminal through system information or a control message (e.g., controlmessage including the Resource-Config information).

The base station may transmit an RRC message or a MAC control messageincluding the Resource-Config information to the terminal. The RRCmessage used for transmitting the Resource-Config information may be aconnection reconfiguration message (e.g., RRCConnectionReconfigurationmessage) used for RRC connection establishment. Alternatively, the RRCmessage used for transmitting the Resource-Config information may betransmitted based on a format of the connection reconfiguration message.

Also, a partial connection reconfiguration message (e.g., a message towhich a delta signaling scheme is applied) including only changedparameters among the parameters included in the connectionreconfiguration message may be generated, and the partial connectionreconfiguration message may be used to transmit the Resource-Configinformation. Alternatively, the base station may generate a separatebeam reconfiguration control message including only the Resource-Configinformation, and may transmit the generated beam reconfiguration controlmessage to the terminal.

Also, when the Resource-Config information indicates a mapping,replacement, or change of a radio resource index (e.g., beam index)according to the beam reconfiguration instead of the radio resourceallocation information (e.g., radio resource configuration information),or when the Resource-Config information indicates activation orinactivation of a radio resource (e.g., beam) instead of the radioresource allocation information (e.g., radio resource configurationinformation), the Resource-Config information may be transmitted to theterminal via a PHY layer control channel (e.g., an indication fieldincluded in the control channel) or a MAC control message.

In the case that the beam problem detection operation, the beam recoveryoperation, and the beam reconfiguration operation are performed mainlyby the MAC layer, the updated Resource-Config information (e.g., changedResource-Config information) may be transmitted to the terminal via aPHY layer control channel or a MAC control message instead of an RRCmessage. A method in which the beam problem detection step S702 to thebeam recovery step S703 are controlled by the MAC layer or a method inwhich the beam problem detection step S702 to the beam reconfigurationstep S704 are controlled by the MAC layer may be considered.

The beam monitoring operation may be performed using specific signalsfor each base station (or beam) in order for the MAC layer to mainlyperform the monitoring operation for the beam problem detectionoperation, the beam recovery operation, and the beam reconfigurationoperation. For example, the terminal may perform the beam monitoringoperation using the PHY layer control channel (e.g., PDCCH, PUCCH) orthe common reference signal instead of the RRC message. In this case,the terminal may perform the beam monitoring operation using thesynchronization signal, the reference signal for the PHY layer controlchannel, or the reference signal for beam sweeping.

The signals described above (e.g., synchronization signal, referencesignal) may be uniquely configured for each base station (or each beam),the terminal may identify each base station or beam using thecorresponding signal, and measure a received signal quality for the basestation or beam. Here, the reference signal for the PHY layer controlchannel may include a reference signal used for demodulating the PHYlayer control channel, a reference signal used for identifying anantenna port, a reference signal for identifying an arrangement of anantenna array for beamforming, or a reference signal used for locationbased services. The reference signal for beam sweeping may be areference signal for beam monitoring operation. The reference signal forthe PHY layer control channel or the reference signal for beam sweepingmay be periodically or aperiodically transmitted in a fixedtime-frequency resource or fixed time-frequency resources.

Accordingly, since the terminal may know a transmission pattern of thereference signal without receiving a signaling message includingconfiguration information of the reference signal described above (e.g.,the message including the changed Resource-Config information), theterminal may perform the beam monitoring operation using the referencesignal in the beam problem detection step S702, the beam recovery stepS703, and the beam reconfiguration step S704.

Beam Recovery Operation (e.g., Recovery Operation of the Same Beam)

When the same beam is successfully recovered by the beam recoveryoperation, the MAC layer of the terminal may transmit informationindicating that the same beam has been successfully recovered to the RRClayer of the terminal. Alternatively, without transmitting informationindicating that the same beam has been successfully recovered, the MAClayer of the terminal may control operations of the MAC layer or the PHYlayer according to the Resource-Config information configured before thebeam recovery operation. When necessary, the MAC layer or the RRC layerof the terminal may generate a control message including the identifierof the terminal, downlink and uplink beam indexes, beam measurementresults, and the like, and may transmit the generated control message tothe base station. Here, the control message may indicate that beamrecovery has been successfully completed. In this case, theResource-Config information configured before the beam recoveryoperation may be reused.

In the beam recovery step S703, an uplink radio resource (or signal)mapped to the synchronization signal, the reference signal for the PHYlayer control channel, or the reference signal for beam sweeping, whichis a search and measurement target, may be configured. For example, amapping relationship between the downlink signal and an uplink RAresource, an SRS, a PHY layer uplink control channel, or a referencesignal for uplink beam sweeping may be defined. In this case, when abeam corresponding to a beam recovery condition is found in the beamrecovery step S703, the terminal may transmit an uplink signalcorresponding to the downlink signal of the found beam to inform thebase station that the beam recovery has been completed successfully.

In the case where the above-described method is used, even when theindex of the recovered beam is not transmitted to the base station afterthe beam recovery has been successfully completed, the base station mayidentify the index of the recovered beam based on the uplink signalreceived from the terminal or a radio resource (e.g., physical resourceblock (PRB)) occupied by the received uplink signal. When necessary, theterminal may transmit a control message including the beam measurementresult to the base station. The control message including the beammeasurement result may be a RA message, a MAC control message or an RRCmessage. The RA message may be a first message (e.g., a RA MSG1)transmitted by the terminal in the RA procedure or a second message(e.g., a RA MSG3) transmitted by the terminal in the RA procedure. Whenthe beam measurement result is transmitted through the RA message, theformat of the RA message may be the same as the format of the MACcontrol message.

When there is no predefined mapping relationship between thesynchronization signal, the reference signal for the PHY layer controlchannel, or the reference signal for beam sweep, and the uplink signalin the beam recovery step S703, the control message indicating thesuccessful completion of the beam recovery may be configured in a formof a RA message, a MAC control message, or an RRC message. In this case,the control message may include the index of the recovered beam, thebeam measurement result, the terminal identifier, and the like.

Even when the same downlink beam is selected as the result of the beamrecovery operation, an uplink beam may be selected as an uplink beamother than the uplink beam used before the beam recovery operation. Ifit is identified that another uplink beam is selected as the result ofthe beam recovery operation, the MAC layer of the terminal may transmitinformation indicating that another uplink beam is selected to the RRClayer of the terminal. In this case, the MAC layer or the RRC layer ofthe terminal may transmit to the base station information indicatingthat the beam recovery operation has been successfully completed,configuration information (e.g., beam index) of the new uplink beamselected in the beam recovery operation, the measurement result of thenew uplink beam, and the like.

The base station may receive the control message from the terminal andconfirm that the beam recovery operation has been successfully completedbased on the control message. Also, the base station may obtainconfiguration information (e.g., beam index) of the new uplink beam, themeasurement result of the new uplink beam, and the like from the controlmessage. In this case, the base station may configure Resource-Configinformation based on one of the following methods.

-   -   Method 1: The base station transmits information indicating        reuse of the Resource-Config information to the terminal.    -   Method 2: The base station generates Resource-Config information        and transmits a control message including the generated        Resource-Config information to the terminal.    -   Method 3: The base station generates a control message including        only parameters changed according to the new uplink beam, among        the parameters in the Resource-Config information, and transmits        the generated control message to the terminal.

The control message according to the Method 1, the Method 2, or theMethod 3 may be transmitted through a PHY layer control channel. In thiscase, the control message may be in a form of a DCI, a UCI, or anindicator (e.g., field). Alternatively, the control message according tothe Method 1, the Method 2, or the Method 3 may be a MAC control messageor an RRC message.

Beam Reconfiguration Operation

The terminal may perform the beam reconfiguration operation (e.g., beammonitoring operation) after the beam recovery operation has failed(e.g., after the beam failure has been determined), and the beamselected by the beam reconfiguration operation may be one of thefollowing beams.

-   -   Case 1: The same beam as the previous serving beam (e.g., the        beam in which a beam failure is determined in the beam recovery        step)    -   Case 2: Another beam of the serving base station (e.g., the base        station to which the beam in which a beam failure is determined        in the beam recovery step belongs)    -   Case 3: Abeam of a base station other than the serving base        station (e.g., the base station to which the beam in which a        beam failure is determined in the beam recovery step belongs)

In Case 1, the terminal may perform the operations specified in the‘recovery operation of the same beam’ described above.

In Case 2, the control message used to change the Resource-Configinformation may be at least one of a PHY layer control channel (e.g.,indication field), a MAC control message, and an RRC message. Here, whena MAC control message or an RRC message is used, a form of a controlmessage applied to a beam change operation (e.g., a beam switchingoperation) in the same base station according to a general procedureother than the beam recovery operation or the beam reconfigurationoperation. In this case, the control message may indicate a change ofthe configuration information of the MAC layer, a change of theconfiguration parameters of the PHY layer control channel, or a changeof the reference signals according to the beam change (e.g., beamswitching).

Here, the configuration information of the MAC layer may beconfiguration parameters in the MACmain_config message among the RRCcontrol messages of the LTE system. The configuration parameters of thePHY layer control channel may be parameters constituting thePhysicalConfigDedicated, PUCCH-Config, RACH-ConfigCommon,RACH-ConfigDedicated, RadioResourceConfigCommon, orRadioResourceConfigDedicated message among the RRC control messages ofthe LTE system. Therefore, the control message for beam switching in thesame base station may be a MAC control message, not an RRC message.

In case 2, the RRC message or the MAC control message for beam switchingin the same base station may indicate a change (e.g., update) of theconfiguration information of the MAC layer or the configurationparameters of the PHY layer control channel constituting theResource-Config information.

In particular, when a MAC control message is used, the Resource-Configinformation for a plurality of beams in the base station may beconfigured by an RRC message in a procedure of establishing an RRCconnection. When the beam is reconfigured, each of the mapping,replacement, or change operation of the radio resource index configuredby the Resource-Config information and the radio resource activation orinactivation operation may be indicated by the MAC control message orthe PHY layer control channel in the RRC connection establishmentprocedure.

Alternatively, the terminal may transmit a MAC control message includinginformation on the target beam selected by the beam monitoring operation(e.g., beam index, beam measurement result) to the base station. Thebase station receiving the information on the target beam from theterminal may operate based on one of the following methods.

-   -   Method A: The MAC layer of the base station may report the        information on the target beam to the RRC layer of the base        station.        -   (Method A-1): The RRC layer of the base station may receive            the information on the target beam from the MAC layer of the            base station, generate the Resource-Config information based            on the information on the target beam, and transmit the            Resource-Config information to the MAC layer of the base            station. The MAC layer of the base station may receive the            Resource-Config information from the RRC layer of the base            station, and transmit a MAC control message including the            Resource-Config information to the terminal.        -   (Method A-2): The RRC layer of the base station may receive            the information on the target beam from the MAC layer of the            base station, generate the Resource-Config information based            on the information on the target beam, and transmit an RRC            message including the Resource-Config information to the            terminal.    -   Method B: The MAC layer of the base station may generate the        Resource-Config information based on the target beam, and        transmit a MAC control message including Resource-Config        information to the terminal. Also, the MAC layer of the base        station may transmit the Resource-Config information to the RRC        layer of the base station.

In case 2, the downlink beam may be changed and the uplink beam may bethe same as the previous uplink beam. In this case, the MAC layer of theterminal may transmit information indicating that the beamreconfiguration operation has been successfully completed, an indicator(e.g., information on the uplink beam) indicating that the same uplinkbeam has been reconfigured by the beam reconfiguration operation, andthe like to the upper layer (e.g., RRC layer) of the terminal.Alternatively, the MAC layer of the terminal may control the functionsof the MAC layer or the PHY layer of the terminal to be performed basedon the configuration parameters of the uplink beam in theResource-Config information that has been already configured.

The MAC layer of the terminal may transmit a control message (e.g., MACcontrol message) indicating that the beam reconfiguration operation hasbeen successfully completed to the base station. Alternatively, the RRClayer of the terminal may transmit a control message (e.g., RRC message)indicating that the beam reconfiguration operation has been successfullycompleted to the base station. Here, the control message may include theidentifier of the terminal, information on the reconfigured beam (e.g.,beam measurement result, beam index), and the like. The base station mayreceive the control message from the terminal, and confirm theinformation on the uplink beam included in the control message (e.g.,the information on the configured beam). When the same uplink beam isreconfigured by the beam reconfiguration operation, the base station maytransmit a control message (e.g., a PHY layer control channel, a MACmessage, an RRC message, or the like) including information indicatingthat the configuration information of the uplink beam in theResource-Config information is reused.

Here, the RRC message may include partial Resource-Config informationincluding only changed parameters by applying a delta signaling scheme.Alternatively, the RRC message may indicate that the configurationinformation of the uplink beam in the Resource-Config information isreused. When a PHY layer control channel (e.g., indicator) or a MACcontrol message is used, the PHY layer control channel or MAC controlmessage may indicate the reuse (e.g., activation) of the Resource-Configinformation.

In Case 3, the terminal may transmit a control message requesting ahandover or a measurement result triggering a handover together with thebeam monitoring result. Upon receiving the control message requesting ahandover or the measurement result triggering a handover, the basestation may perform a handover procedure. In this case, the terminal mayreceive the Resource-Config information of the target base station fromthe serving base station or the target base station.

Meanwhile, the beam problem detection step S702, the beam recovery stepS703, the beam reconfiguration step S704, and the radio linkre-establishment step S705 described above with reference to FIG. 7 maybe controlled partially by each of the layers belonging to the terminalor the base station. For example, the steps illustrated in FIG. 7 may becontrolled by each of the layers as described below.

FIG. 8 is a flow chart illustrating a first embodiment of a beammanagement procedure in a communication system.

Referring to FIG. 8, the beam management procedure may be controlled byat least one of a MAC layer and an RRC layer. For example, the beammanagement procedure may be as shown in Table 2 below.

TABLE 2 Beam Beam Radio link Beam problem recovery reconfigura-re-establish- detection step step tion step ment step Method 1 MAC layerMAC layer RRC layer RRC layer Method 2 MAC layer MAC layer MAC layer RRClayer Method 3 RRC layer RRC layer RRC layer RRC layer

In Method 1, the beam problem detection step and the beam recovery stepmay be controlled by the MAC layer, and the beam reconfiguration stepand the radio link re-establishment step may be controlled by the RRClayer. In Method 2, the beam problem detection step, the beam recoverystep, and the beam reconfiguration step may be controlled by the MAClayer, and the radio link re-establishment step may be controlled by theRRC layer. In Method 3, the beam problem detecting step, the beamrecovery step, the beam reconfiguration step, and the radio linkre-establishment step may be controlled by the RRC layer.

The following operations may be further applied when the MAC layer ofthe terminal transmits at least one of the management result of theradio link and the result of the beam monitoring operation to the RRClayer of the terminal or when the terminal reports the same to the basestation.

When a beam problem is detected based the IS_Ind or OoS_Ind obtainedfrom the PHY layer or information obtained by another method, the PHYlayer or MAC layer of the terminal may report information indicatingthat the beam problem has been detected to the upper layer (e.g., MAClayer or RRC layer). Also, the terminal may transmit the informationindicating that the beam problem has been detected to the base stationby using an available uplink channel (e.g., PUCCH or PUSCH) or a RAchannel (e.g., physical RA channel (PRACH)).

Upon receiving the information indicating that the beam problem has beendetected from the terminal, the base station may configureResource-Config information for another beam or a plurality of beams,and transmit the Resource-Config information to the terminal. Theterminal may receive the Resource-Config information (e.g., updated orchanged Resource-Config information) from the base station, and performa beam monitoring operation using the Resource-Config information.

When the same beam is recovered by the beam recovery operation (S803 toS804), the MAC layer of the terminal may transmit information indicatingthat the same beam has been successfully recovered by the beam recoveryoperation to the RRC layer of the terminal. In this case, the terminalmay not transmit to the base station the information indicating that thesame beam has been successfully recovered by the beam recoveryoperation.

On the other hand, when the beam recovery fails in the beam recoveryoperation (S803 to S804), the MAC layer of the terminal may perform abeam reconfiguration operation (S805 to S806). When the beamreconfiguration operation has been successfully completed, the MAC layerof the terminal may transmit information indicating that the beamreconfiguration operation has been successfully completed to the RRClayer of the terminal. Also, the terminal may transmit a control messageincluding the result of the beam reconfiguration operation to the basestation in the following cases.

-   -   A case in which the same beam is reconfigured after expiration        of a predetermined timer (e.g., T_(Info-Update)). Here, a        setting value for the T_(Info-Update) may be transmitted to the        terminal via system information or a dedicated control message    -   A case in which another beam is reconfigured as the beam (e.g.,        uplink beam or downlink beam) in the beam reconfiguration        operation

In this case, the MAC layer or the RRC layer of the terminal maygenerate a control message to be transmitted to the base station. Whenthe information indicating that the beam reconfiguration operation hasbeen successfully completed is received from the terminal after theexpiration of T_(Info-Update), the base station may reconfigureparameters required to be changed or updated among the parameters in theResource-Config information, and transmit a control message includingthe reconfigured parameters to the terminal.

Here, the control message may be a control message used for the beamswitching operation at the same base station. The control message forthe beam switching operation may be a message including theResource-Config information or MAC layer configuration information, andmay be configured in a form of an RRC message or a MAC control message.The control message may include parameters necessary for the beammonitoring operation (S801 to S802), the beam recovery operation (S803to S804), the beam reconfiguration operation (S805 to S806), and theradio link re-establishment operation (S807 to S808) for radio linkmanagement.

Alternatively, the control message (e.g., control signaling) used in thebeam switching operation may be transmitted over a PHY layer controlchannel. For example, a signal configured for radio link management, anindicator for indicating activation of radio resources, or an indicatorfor indicating inactivation for radio resources may be transmittedthrough a PHY layer control channel.

When the result of the beam monitoring operation (S801 to S802), theresult of the beam recovery operation (S803 to S804), the result of thebeam reconfiguration operation (S805 to S806), or the result of theradio link re-establishment operation (S807 to S808) are obtained fromthe terminal, the base station may transmit, to the terminal, the signalconfigured for radio link management, the indicator for indicatingactivation of radio resources, or the indicator for indicatinginactivation for radio resources by using a PHY layer control channel.

Upon receiving the indicator for indicating activation or inactivationfor radio resources from the base station through the PHY layer controlchannel, the terminal may perform a beam management operation for thebeam monitoring operation (S801 to S802) by activating or inactivatingthe radio resources.

When the beam recovery or beam reconfiguration to a beam of another basestation other than the serving base station has been completed throughthe beam management operation, the terminal may transmit a controlmessage requesting a handover. Upon receiving information indicatingthat the beam recovery or beam reconfiguration to the beam of anotherbase station other than the serving base station has been completed, theserving base station may initiate (e.g., trigger) a handover procedure.Alternatively, the base station may transmit a control messagerequesting to initiate a handover procedure to the terminal.

Radio Link Re-Establishment Operation

When the beam reconfiguration operation has not been successfullycompleted, the terminal may determine a radio link failure (RLF). Inthis case, the terminal may perform the radio link re-establishmentoperation (S705 in FIG. 7, S807 to S808 in FIG. 8). In this case, theterminal may perform a beam search and measurement operation (e.g., beamsweeping operation) to detect a beam that meets a radio linkre-establishment condition. The terminal may perform beam the search andmeasurement operation on beams of the serving base stations as well asbeams of other base stations.

If a beam meeting the radio link re-establishment condition is detectedbefore expiration of a predetermined timer, the terminal may perform theradio link re-establishment operation with the detected beam. Here, asetting value for the predetermined timer may be transmitted from thebase station to the terminal via a PHY layer control channel, a MACcontrol message or an RRC message. The base station performing the stepS705 (e.g., the steps S807 to S808) with the terminal may be the same asthe base station performing the steps S701 to S704 (e.g., the steps S801to S806). Alternatively, the base station performing the step S705(e.g., the steps S807 to S808) with the terminal may be different fromthe base station performing the steps S701 to S704 (e.g., the steps S801to S806).

In the radio link re-establishment step, the base station may transmit acontrol message (e.g., a control message for connection establishment)including Resource-Config information to the terminal. The terminal mayreceive the control message including the Resource-Config informationfrom the base station, and configure parameters based on theResource-Config information included in the control message.

On the other hand, when a beam meeting the radio link re-establishmentcondition is not detected within the time according to the predeterminedtimer, the terminal may determine that the radio link re-establishmentoperation has failed. In this case, the operational state of theterminal may transition from the RRC connected state to the RRC inactivestate or the RRC idle state.

In the case that the RRC layer controls the procedure shown in FIG. 7 or8 instead of the MAC layer (e.g., Method 3 of Table 2), the information(e.g., information related to the beam problem detection step,information related to the beam recovery step, information related tothe beam reconfiguration step, etc.) generated and acquired at the MAClayer according to the Method 1 or 2 of Table 2 may be transmitted tothe RRC layer. For example, the OoS_Ind or IS_Ind generated by the PHYlayer of the terminal may be transmitted to the RRC layer through theMAC layer. When the Method 3 of Table 2 is performed, the RRC layerinstead of the MAC layer may mainly perform the procedure shown in FIG.7 or 8.

On the other hand, the management operation of the beam/radio link maynot be performed according to the order shown in FIG. 7 or FIG. 8. Also,when the management operation of the beam/radio link is performed, allthe steps shown in FIG. 7 or 8 may be selectively performed, some stepsshown in FIG. 7 or 8 may be performed in parallel, and some of the stepsshown in FIG. 7 or 8 may be integrated into a single step.

For example, the beam recovery operation (S703 in FIG. 7 or S803 to S804in FIG. 8) and the beam reconfiguration operation (S704 in FIG. 7 orS805 to S806 in FIG. 8) may be integrated into a single operation.Alternatively, the beam recovery operation (S703 in FIG. 7 or S803 toS804 in FIG. 8) may be performed in parallel with the beamreconfiguration operation (S704 in FIG. 7 or S805 to S806 in FIG. 8).When the beam recovery operation and the beam reconfiguration operationare integrated into a single operation, the beam recovery operation maybe merged into the beam reconfiguration operation, or the beamreconfiguration operation may be merged into the beam recoveryoperation. In this case, one timer and reference value may be usedinstead of the timers and reference values for the beam recoveryoperation and the beam reconfiguration operation. For example, one ofthe above-described T_(BR) and T_(BP) may be used.

The beam recovery operation and the beam reconfiguration operation maybe performed for the beam belonging to the serving base station and theradio link re-establishment operation may be performed for the beambelonging to the base station other than the serving base station. Inthis case, the control message used for configuring the Resource-Configinformation in the procedure shown in FIG. 7 or 8 may be configured in aform of a PHY layer control channel, a MAC control message, or an RRCmessage.

Also, the procedure shown in FIG. 7 or 8 may be applied even when one ormore configured beams (e.g., serving beam) are used between the basestation and the terminal. In the procedure shown in FIG. 7 or 8, thebase station may control the terminal to report statistical historyinformation for each of the beam problem detection operation, the beamrecovery operation, the beam reconfiguration operation, and the radiolink re-establishment operation.

For example, the base station may control the terminal to report atleast one of a received signal quality of the beam, a beam index, anidentifier of the base station, a completion time of beam recovery froma time point at which the beam problem is detected, or a time requireduntil a completion time of beam reconfiguration, a time required until acompletion time of radio link re-establishment from a time point atwhich the radio link failure is determined, and a position of theterminal.

Also, the terminal may report at least one of a frequency of beamproblem detections, a frequency (or success rate) of beam recoverysuccesses, and a frequency (or failure rate) of beam recovery failuresaccording to the configuration of the base station. For this purpose,the base station may configure a measurement interval (or duration), ameasurement time, and a reporting time for calculating the correspondingreport values. The base station may also define an event that triggersthe measurement or the reporting. The terminal may perform themeasurement according to the condition configured by the base station,and report the measurement result using a MAC control message or an RRCmessage. The terminal may transmit to the base station measurement orreport parameters configured by the base station in association with aspecific event when the specific event occurs in each of the beamproblem detection operation, the beam recovery operation, the beamreconfiguration operation, and the radio link re-establishmentoperation. Alternatively, the terminal may transmit an event occurringin a predetermined interval (or duration) and a parameter (e.g., anaverage value or a standard deviation of the parameter) related to theevent to the base station according to a preset reporting cycle.Alternatively, when a preset reporting condition is met, the terminalmay transmit to the base station an event occurring in a predeterminedinterval (or duration) and a parameter (e.g., an average value or astandard deviation of the parameter) related to the event.

On the other hand, the beam management operation may not be associatedwith the radio link management operation. Here, the beam managementoperation may include the beam monitoring operation, the beam problemdetection operation, the beam failure declaration operation, the beamrecovery operation, the beam reconfiguration operation, the beamre-pairing operation, and the like. The radio link management operationmay include the radio link monitoring operation, the radio link problemdetection operation, the radio link failure declaration operation, theradio link recovery operation, the radio link re-establishmentoperation, and the like.

In the case that the beam management operation is distinguished from theradio link management operation, the beam failure or the beam recoveryfailure according to the beam management operation may not be associatedwith the radio link failure. Also, the beam failure or the beam recoveryfailure according to the beam management operation may not trigger theradio link re-establishment operation.

In the radio link management operation, the PHY layer of the terminalmay transmit the IS_Ind or the OoS_Ind to the upper layer (e.g., MAClayer or RRC layer), and the upper layer may detect a problem of theradio link based on the OoS_Ind or the IS_Ind. Alternatively, whensuccessive RA attempts fail or when a reference condition according to aretransmission failure is met, the terminal may determine that a radiolink problem has been detected. In this case, the terminal may declare aradio link failure (RLF).

The terminal may perform the beam management operation independently ofthe radio link management operation. For example, when a beam problem isdetected based on the error rate of the PDCCH or when a beam failure isdeclared based on the error rate of the PDCCH, the terminal may performthe beam recovery operation and the beam reconfiguration operation(e.g., beam re-pairing operation). In the case that the beam failure isdeclared, the beam recovery fails, or the beam reconfiguration fails,the terminal may not trigger the radio link re-establishment andreconfiguration operation in the following cases.

-   -   Case 1: A case in which downlink synchronization is maintained        according to a criterion of the radio link management operation    -   Case 2: A case in which an RLF is not declared according to a        criterion of the radio link management operation or a case in        which a condition for declaring an RLF is not met according to a        criterion of the radio link management operation (e.g., a case        in which the number of RA attempts or retransmission attempts is        equal to or less than a reference value)

Therefore, even when the beam failure is declared or the beam recoveryfails, the terminal may not perform the radio link re-establishment andreconfiguration operation due to the beam failure or the beam recoveryfailure before triggering the declaration of an RLF according to acriterion of the radio link management operation or the radio linkre-establishment and reconfiguration operation.

However, when a problem of a core radio link is detected by the radiolink management operation, or when a failure of a core radio link isdeclared by the radio link management operation, the terminal mayperform the beam recovery operation even before the beam problemdetection or the beam failure declaration according to the beammanagement operation. Here, the core radio link may be a radio linkestablished and managed between the base station and the terminal. Forexample, the core radio link may be as follows.

-   -   A radio link used for transmitting and receiving a downlink PHY        layer control channel or an uplink PHY layer control channel for        the terminal    -   A radio link which is a reference for maintaining downlink        synchronization or uplink synchronization    -   A radio link in which a CORESET is configured in a NR system to        which a radio resource structure supporting multiple        numerologies    -   A radio link for a primary cell (e.g., PCell or PSCell) when a        carrier aggregation (CA) function or a dual connectivity (DC)        function is supported

Here, the radio link may be a PHY layer radio channel, a beam to whichbeamforming is applied, a part of the system bandwidth (e.g., BWP of theNR system) of the base station (e.g., cell), or the like. The radio linkmay be a radio link in which radio resources allocated to the terminalexist, and may be an object of the radio link management operation.

Also, the entity performing the beam management operation and the entityperforming the radio link management operation may be distinguished. Forexample, in the beam management operation, the beam problem detectionstep, the beam failure declaration step, and the beam recovery step maybe mainly performed by the PHY layer of the terminal. In the radio linkmanagement operation, the radio link failure declaration step, the radiolink recovery step, and the radio link reconfiguration andre-establishment step may be performed by the MAC layer or the RRC layerof the terminal. That is, the MAC layer or the RRC layer of the terminalmay perform the radio link management operation based on the informationobtained from the PHY layer of the terminal.

When the beam management operation is primarily performed by the PHYlayer of the terminal, the PHY layer of the terminal may perform thebeam recovery operation when the beam problem is detected. When the beamfailure or the beam recovery failure is identified, the PHY layer of theterminal may declare the beam failure or the beam recovery failure andmay transmit the result of the declaration to the upper layer (e.g., MAClayer or RRC layer) of the terminal. Upon receiving informationindicating the beam failure or the beam recovery failure from the PHYlayer of the terminal, the upper layer of the terminal may identifywhether an RLF condition according to the radio link managementoperation is met or not, and maintain functions of the upper layer whenthe RLF condition is not met. In this case, the terminal may monitor aPDCCH and perform a beam search operation (e.g., beam sweepingoperation) in the current frequency band and another frequency band(e.g., BWP).

When the beam failure or the beam recovery failure is finallydetermined, the terminal may not perform a reception operation of thedownlink channel (e.g., PDCCH, PDSCH, etc.) and may restrictedly performa transmission operation of the uplink channel. For example, theterminal may not perform an uplink channel transmission operation excepttransmission of a RA preamble and transmission of a control messagethrough a PUCCH for reporting the beam recovery failure.

Also, the upper layer of the terminal may trigger the PHY layer of theterminal to perform a monition and search operation on a referencesignal of the serving beam (e.g., reference signal assigned to theterminal), a common reference signal for initial access procedure orinitial cell search procedure, a reference signal for management of abeam or a radio link, or a burst of synchronization signals. When theRLF condition according to the radio link management operation is met,the functions of the upper layer of the terminal may be reset and theradio link reconfiguration and re-establishment operation may beperformed.

A method of configuring parameters for beam measurement and radiochannel measurement and an effective control method may be required forthe beam management operation or the radio link management operation.For example, measurement procedures and measurement result reportingprocedures for the configured beam, the active beam, the measurementtarget beam, and the neighbor beam may be required for control of thebeam management operation, an operation of determining and overcoming abeam blockage by obstacles on the radio link, and the beam switchingoperation.

The base station or terminal may measure the reference signal of theradio channel (e.g., beam) continuously or discontinuously. The terminalmay report the measurement result based on the parameters configured forthe measurement or the measurement result reporting. In the measurementand reporting procedure of the reference signal of the radio channel(e.g., beam), a reception quality of the reference signal or a change inthe reception quality per unit time may be measured, and the measurementresult may be reported. For example, when the change in the receptionquality of the reference signal corresponds to a preset condition (e.g.,a sudden change in the reception quality) in a preset measurementinterval (or duration) (e.g., a measurement unit time), the beammanagement operation may be controlled to be performed.

For example, when the reception quality of the reference signal is lessthan or equal to a preset reference value, or when the reception qualityof the reference signal is kept to be equal to or less than a presetreference value for a predetermined time period (e.g., a time periodaccording to a timer), it may be determined that a beam or radio linkproblem, a beam or radio link failure, or a beam blockage has occurred.Also, when the reception quality of the reference signal exceeds apreset reference value, or when the reception quality of the referencesignal is kept to be greater than a preset reference value for apredetermined time period (e.g., a time period according to a timer), asuccess of the beam or radio link recovery, a success of the beamswitching operation, or a release of the beam blockage may bedetermined.

For example, the base station or the terminal may measure the receptionquality of the reference signal for controlling each of the beamblockage determination operation and the beam switching operation. Whena deterioration rate of the measured reception quality (e.g., adeterioration rate of the reception quality measured per unit time) isequal to or greater than a preset reference value or when thedeterioration rate of the measured reception quality is kept to be equalto or less than a preset reference value for a predetermined time period(e.g., a time period according to a timer), the terminal or the basestation may determine that a beam blockage has occurred. In this case,the base station or the terminal may perform an inactivation operationor a beam switching operation on the beam in which the beam blockage hasoccurred.

For example, when the timer is set to 2 seconds and the preset referencevalue is 10 dB, the timer may be reset to 0 if the deterioration rate ofthe reception quality of the reference signal is less than 10 dB for thetime period according to the timer. On the other hand, when the timer isset to 2 seconds and the preset reference value is 10 dB, the terminalor the base station may determine that a beam blockage has occurred ifthe deterioration rate of the reception quality of the reference signalis equal to or greater than 10 dB for the time period according to thetimer. In this case, the base station or the terminal may perform a beaminactivation operation or a beam switching operation on the beam inwhich the beam blockage has occurred. Also, the timer may be reset to‘0’, or may be stopped.

Alternatively, when an enhancement rate of the reception quality of thereference signal is equal to or greater than a preset reference value,or when the enhancement rate of the reception quality of the referencesignal is kept to be equal to or greater than a preset reference valuefor a predetermined time period (e.g., a time period according to thetimer), the base station or the terminal may determine that the beamblockage has been released. In this case, the base station or theterminal may activate the beam in which the beam blockage has beenreleased. Alternatively, the base station or the terminal may switch thecurrent beam to the beam for which the beam blockage is determined to bereleased. Here, the timer may be used for determining whether the beamblockage is releaser or not, or for controlling the beam switchingoperation.

If the enhancement rate of the reception quality of the reference signaldeviates from a preset reference value before the expiration of thetimer, the timer may be restarted. For example, when the timer is set to2 seconds and the preset reference value is 10 dB, the timer may bereset to 0 if the enhancement rate of the reception quality of thereference signal is equal to or less than 10 dB. On the other hand, ifthe enhancement rate of the reception quality of the reference signalexceeds 10 dB before the expiration of the timer, it may be determinedthat the beam blockage has been released. In this case, the base stationor the terminal may reset the timer to 0 or stop the timer. Also, thebase station or the terminal may perform a beam activation operation ora beam switching operation.

The parameter used for determining the deterioration rate and theenhancement rate of the reception quality of the reference signal may bethe ‘preset reference value’ or the ‘preset reference value+timer’. Thebase station may transmit the parameter (e.g., the preset referencevalue, a setting value for the timer) used for determining thedeterioration rate and the enhancement rate to the terminal throughsystem information or a control message.

The above-described determination operation and the beam switchingoperation for the beam blockage based on the deterioration rate and theenhancement rate of the reception quality may be applied to the beam orradio link management operation (e.g., the beam or radio link problemdetection operation, the beam or radio recovery operation, the beam orradio link failure declaration operation, etc.). However, the parameters(e.g., preset reference value, timer) used for determining thedeterioration rate and the enhancement rate may be configured accordingto a purpose of each of the operations included in the beam or radiolink management operation.

The parameters for measuring the reception quality of the referencesignal in the beam or radio link management operation may include ameasurement unit time, a measurement interval (or duration), a presetreference value for the deterioration rate of the reception quality ofthe reference signal, a preset reference value for the enhancement rateof the reception quality of the reference signal, and the like. Each ofthe measurement unit time and the measurement interval (or duration) maybe configured as an absolute time (e.g., in units of millisecond (ms) orsecond, etc.), or in units of transmission timing intervals (TTIs),symbols, mini-slots, subframes, frames, scheduling periods, or the like.For example, each of the measurement unit time and the measurementinterval (or duration) may be configured according to a configured cycleof a radio channel, an operation cycle of the base station, or anoperation cycle of the terminal. The preset reference value for each ofthe deterioration rate and the enhancement rate of the reception qualityof the reference signal may be configured to an absolute value (dBm) ora relative value (dB).

The reception quality of the reference signal may be a measurementresult of the synchronization signal (e.g., SS/PBCH block), CSI-RS,phase tracking-reference signal (PT-RS), SRS, DMRS, or the like. Thereception quality of the reference signal may be represented asreference signal received power (RSRP), reference signal receivedquality (RSRQ), received signal strength indicator (RSSI),signal-to-noise ratio (SNR), signal-to-interference ratio (SIR), or thelike.

The measurement operation for the beam or radio link managementdescribed above may be performed by the base station or the terminal.Each of the base station and the terminal may perform the measurementoperation according to the parameters configured for the measurementoperation. The terminal may report the measurement result to the basestation according to the parameters configured for the measurementreporting.

When the reception quality of the measured reference signal satisfiesthe preset condition (e.g., ‘preset reference value’ or ‘presetreference value+timer’), the base station may start the beam or radiolink management operation, the beam switching operation, the beamactivation or inactivation operation according to the beam blockage, orthe like, and may transmit a control message including information forthe started operation to the terminal.

Also, when the reception quality of the measured reference signalsatisfies the preset condition (e.g., ‘preset reference value’ or‘preset reference value+timer’), the terminal may report the measurementresult to the terminal. In this case, the terminal may transmit to thebase station a control message indicating that the beam or radio linkmanagement operation, the beam switching operation, the beam activationor inactivation operation according to the beam blockage, or the like isstarted.

The PHY layer, the MAC layer, and the RRC layer of each of the basestation and the terminal may exchange control information for themeasurement operation, the measurement reporting operation, the beam orradio link management operation, the beam switching operation, the beamactivation or inactivation operation according to the beam blockage, orthe like.

For example, the PHY layer may transmit the measurement result to theupper layer (e.g., MAC layer, RRC layer). Upon receiving the measurementresult from the PHY layer, the MAC layer of the base station maygenerate a MAC control message for the beam or radio link managementoperation, the beam switching operation, the beam blockage determinationoperation, or the like when the measurement result satisfies the presetcondition, and may transmit the MAC control message to the terminal.Alternatively, when the measurement result is received from the PHYlayer, the MAC layer may transmit the measurement result to the RRClayer.

When the measurement result is received from the lower layer (e.g., PHYlayer, MAC layer), the RRC layer of the base station may transmit to theterminal a control message instructing to perform the beam or radio linkmanagement operation, the beam switching operation, the beam blockagedetermination operation, or the like. Alternatively, the RRC layer ofthe base station may transmit to the lower layer of the base station(e.g., PHY layer, MAC layer) control information instructing to performthe beam or radio link management operation, the beam switchingoperation, the beam blockage determination operation, or the like.

Here, each of a report message including the measurement result and thecontrol message requesting to perform the beam or radio link managementoperation, the beam switching operation, or the beam activation orinactivation operation according to the beam blockage may be a PHY layercontrol message, a MAC control message (e.g., MAC control PDU), or anRRC message. The PHY layer control message may be transmitted through aPDCCH, a PUSCH, or a common channel. The PHY layer control message maybe a signal, at least one symbol, etc. of a control channel.

The control procedure for the beam blockage determination operation, thebeam switching operation, and the beam activation or inactivationoperation described above may be performed in conjunction with the beamor radio link management operation shown in FIG. 7 or FIG. 8.Alternatively, the control procedure for the beam blockage determinationoperation, the beam switching operation, and the beam activation orinactivation operation described above may be performed independently ofthe beam or radio link management operation shown in FIG. 7 or FIG. Thebeam switching operation within the system band of the same base stationmay mean a switching operation of a frequency band (e.g., BWP) withinthe system bandwidth.

Each of the beam configuration information, the beam index mappinginformation, the configuration information of the reserved beam (e.g.,candidate beam), the configuration information for the beam recoveryoperation, the configuration information for the beam reconfigurationinformation, the control message indicating that the beam recoveryoperation has been successfully completed, the control messageindicating the beam reconfiguration operation has been successfullycompleted, the control message for the measurement result reporting, andthe control message for the beam sweeping operation result reporting mayinclude at least one of the following parameters.

-   -   Identifier of a cell or a BWP related to a BWP control operation    -   Configuration parameters of reference signals for the beam        management operation or the beam measurement operation. The        configuration parameters may include at least one of the flowing        parameters.    -   Radio resource allocation parameter for reference signals (e.g.,        allocation information of time-frequency resources    -   Index for identifying reference signals (e.g., identifier)    -   Parameter indicating mapping relationship of reference signals

The beam management operations described above may be configured andcontrolled to take into account a discontinuous reception (DRX)operation or a discontinuous transmission (DTX) operation performed atthe terminal to reduce power consumption. The terminal performing theDRX operation may perform a reception operation in a predetermined timeduration (e.g., ‘on time’ or ‘active time’) according to a DRX cycle,and may not perform a reception operation in a sleep duration (e.g.,‘DRX off time’). The terminal performing the DTX operation may perform atransmission operation in a predetermined time duration (e.g., ‘on time’or ‘active time’) according to a DTX cycle, and may not perform atransmission operation in a sleep duration (e.g., ‘DTX off time’).

The DRX operation or the DTX operation may affect the beam managementoperation of the terminal. In this case, each of the beam monitoringoperation for beam management, the beam problem detection operation, thebeam failure declaration operation, the beam recovery operation, thebeam reconfiguration operation, and the beam pairing operation may beselectively restricted by the DRX operation or the DTX operation.Alternatively, the beam monitoring operation for beam management, thebeam problem detection operation, the beam failure declarationoperation, the beam recovery operation, the beam reconfigurationoperation, and the beam pairing operation may all be stopped by the DRXoperation or the DTX operation. For the DRX operation or the DTXoperation, the parameters for each of the beam monitoring operation forbeam management, the beam problem detection operation, the beam failuredeclaration operation, the beam recovery operation, the beamreconfiguration operation, and the beam pairing operation may be resetor reconfigured. Also, the timer for the beam management operation maybe stopped, reset, or reconfigured.

For example, when the terminal performs the DRX operation, when theterminal enters the sleep duration according to the DRX cycle, when theterminal performs the DTX operation, or when the terminal enters thesleep duration according to the DTX cycle, the terminal may beconfigured or controlled not to perform some or all of the functions(e.g., the beam problem detection operation, the beam failuredeclaration operation, the beam recovery operation, the beamreconfiguration operation, etc.) of the beam management operation.

Here, by stopping a timer for a specific operation or inactivating thespecific operation, all the functions of the beam management operationor some of the functions of the beam management operation may beconfigured or controlled not to be performed. In the case that the timerfor the specific operation is stopped or the specific operation isinactivated, the specific operation may be performed again when theterminal goes out of the sleep duration according to the DRX cycle, whenthe terminal goes out of the sleep duration according to the DTX cycleor when the terminal enters the active time. In this case, the timer forthe specific operation may be started or restarted, and counterparameters for the beam management operation may be reset or restartedfrom the stopped value.

The activation or inactivation of all or some of the functions of thebeam management operation according to the DRX or DTX operation may beindependently controlled or configured according to the DRX cycle, theDTX cycle, or the movement speed of the terminal (e.g., movement state).

When the DRX cycle, the DTX cycle, or the movement speed of the terminalsatisfies a preset reference condition, all or some of the functions ofthe beam management operation may be inactivated. For example, when theDRX cycle or DTX cycle is equal to or longer than a predetermined cycle,all or some of the functions of the beam management operation may beinactivated. On the other hand, when the DRX cycle or DTX cycle isshorter than a predetermined cycle, all or some of the functions of thebeam management operation may be activated. The preset referencecondition (e.g., cycle) may be transmitted from the base station to theterminal through system information or an RRC control message.

When the movement speed of the terminal is equal to or greater than apreset speed, all or some of the functions of the beam managementoperation may be inactivated. On the other hand, when the movement speedof the terminal is less than a preset speed, all or some of thefunctions of the beam management operation may be activated. The presetreference condition (e.g., speed) may be transmitted from the basestation to the terminal through system information or an RRC controlmessage.

When necessary, for the activation or inactivation of all or some of thefunctions of the beam management operation, all of the DRX cycle, theDTX cycle, and the movement speed of the terminal may be considered. Inorder not to perform the beam problem detection operation, the beamrecovery operation, or the beam recovery failure declaration operation,the terminal may request the base station to perform a beam switchingoperation based on the beam monitoring result or the beam measurementresult. For this, an event for determining whether to perform a beamswitching operation may be configured in the terminal, and the parameterfor configuring the reference value for the quality of the beam or radiolink may be applied.

The parameter for configuring the event and the reference value may beused for the terminal to determine whether to perform the beam switchingoperation by comparing a quality of a serving beam (e.g., active beam orscheduling beam) or a serving radio link (e.g., active radio link or ascheduling radio link), which is currently used for packet transmissionand reception, with qualities of other beams or radio inks based on thereference signal (e.g., SS/PBCH block, CSI-RS, PT-RS, positioningreference signal (PRS), etc.). Here, the quality of the beam or radiolink may be represented as a channel quality indicator (CQI), a channelstate indicator (CSI), a received signal strength indicator (RSSI), areference signal received power (RSRP), a reference signal receivedquality (RSRQ), or the like.

The terminal may transmit information requesting initiation of the beamswitching operation to the base station using a PUCCH or a MAC controlmessage. Here, each of the PUCCH or the MAC control message may includea bit (e.g., parameter) indicating the initiation of the beam switchingoperation, an identifier (e.g., index) indicating the beam, anidentifier (e.g., index) of a reference signal having a mappingrelationship with the beam For example, an index), and the like. Also,each of the PUCCH or the MAC control message may further include anidentifier indicating a BWP. In order to request the initiation of thebeam switching operation, the terminal may transmit to the base stationa RA preamble having a mapping relationship with the beam (e.g.,reference signal) for which switching is requested, an index of the RApreamble, or a radio resource index of the RA preamble (e.g., anidentifier for identifying a radio resource of the RA preamble).

Upon receiving the information requesting the initiation of the beamswitching operation from the terminal, the base station may transmit tothe terminal a control message indicating whether the informationrequesting the initiation of the beam switching operation is received ornot. Alternatively, the base station may perform the beam switchingoperation requested by the terminal without transmitting the controlmessage indicating whether the information is received or not, andtransmit signals to the terminal using the switched beam. Alternatively,when the beam switching operation has been completed, the base stationmay transmit a control message including information indicating that thebeam switching operation has been completed to the terminal using thecurrent serving beam. Thus, after transmitting the informationrequesting the initiation of the beam switching operation, the terminalmay receive necessary control messages or packets from the base stationby monitoring the current serving beam or the beam for which switching,is requested (e.g., a switching, target beam).

Also, when a plurality of cells provide a communication service to theterminal using a carrier aggregation (CA) function, the beam managementoperation shown in FIG. 7 or 8 may be applied to each of a primary cell(PCell) and a secondary cell (SCell). The beam management operation ofthe terminal may be independently applied to each of the primary celland the secondary cell.

The cells supporting the independent beam management operation and theCA, function may perform additional operations for the beam managementoperation of the secondary cell. For example, when a beam problem of thesecondary cell is detected according to the beam management operation,the terminal may transmit to the primary cell information indicatingthat the beam problem of the secondary cell has been detected beforeperforming the beam failure declaration operation or the beam recoveryoperation. The transmission operation of the information indicating thatthe beam problem of the secondary cell has been detected may beperformed independently of each of the beam failure declarationoperation and the beam recovery operation for the secondary cell. Also,the terminal may transmit information for identifying the beam in whichthe beam problem is detected in the secondary cell, information on atime elapsed from the time when the beam problem is detected in thesecondary cell, and the like by applying the above-describedconfiguration parameters.

As another method, when the beam problem is detected in the secondarycell, the terminal may define a timer (e.g., T_(BR)) or another timer(e.g., a timer for Scell beam recovery (T_(S-BR))) for the beam recoveryoperation of the secondary cell, and may perform the beam recoveryoperation before expiration of the corresponding timer (i.e., the T_(BR)or the T_(S-BR)). When a beam failure is declared as a result of thebeam recovery operation for the secondary cell, the terminal maytransmit a control message including information indicating that thebeam failure has been declared at the time of the declaration of thebeam failure.

The control message transmitted by the terminal to the primary cell forthe beam problem detection operation or the beam recovery operation ofthe secondary cell may be a control field of a PHY layer controlchannel, a MAC control element, or an RRC message. The control messagemay include an identifier of a cell performing the beam problemdetection operation and the beam recovery operation, information foridentifying the corresponding beam (e.g., the beam in which the problemis detected), a measurement result of the corresponding beam, ameasurement result of a candidate beam, information indicating whetheror not a condition for performing a non-contention-based RA procedure issatisfied, a time point at which the beam problem is detected, a timeelapsed from a time point at which the beam recovery operation isstarted, and the like. Also, the terminal may transmit a control messagerequesting inactivation of the secondary cell in which the beam problemis detected to the primary cell.

Upon receiving the control message indicating the beam problemdetection, the beam recovery operation, the beam recovery failure, thebeam failure declaration, or the request to inactivate the secondarycell from the terminal, the primary cell may inactivate the secondarycell indicated by the control message, and may transmit a controlmessage indicating that the secondary cell is inactivated to at leastone of the secondary cell and the terminal.

Also, the primary cell or the secondary cell may allocate an RA resourcefor performing a non-contention-based RA procedure or a contention-basedRA procedure for one or more serving beams (e.g., configured beams,candidate beams) to the terminal. Here, the RA resource may beconfiguration parameters for PRACH transmission. For example, the RAresource may indicate an RA preamble index, masking information, apreamble format for the PRACH transmission, a time-frequency resource,and the like.

The terminal having transmitted the control message indicating the beamproblem detection, the beam recovery operation, the beam recoveryfailure, or the beam failure declaration for the secondary cell maydetermine that the corresponding secondary cell is inactivated, andreconfigure the parameters for the corresponding secondary cell.Alternatively, when the control message indicating the inactivation ofthe secondary cell is received from the primary cell, the terminal mayperform an operation according to the control message received from theprimary cell. Upon receiving information on the RA resource forperforming a contention-based RA procedure or a non-contention-based RAprocedure from the primary cell or the secondary cell, the terminal mayperform a contention-based RA procedure or a non-contention-based RAprocedure by using the RA resource, thereby performing the beam recoveryoperation for the secondary cell.

Also, in the beam recovery operation for the secondary cell, theterminal may perform the RA procedure in the secondary cell. In the beamrecovery operation after detecting the beam problem, the terminal maymonitor/measure the beam of the secondary cell. In the case that thebeam which satisfies with the criterion of the beam recovery (e.g., beamconfiguration) by monitoring/measuring the beam of the secondary cell isdetected, the terminal may perform the RA procedure in the secondarycell using the RA resources corresponding to the detected beam.

Here, the RA procedure may be a contention-based RA procedure or anon-contention-based RA procedure. The RA resource (e.g., PRACHresource) for the non-contention-based RA procedure may be obtained froma response message to a CA connection configuration step or thereporting of the beam problem detection of the secondary cell.

When the non-contention-based RA procedure fails or a referencecondition for the non-contention-based RA procedure is not satisfiedafter the detection of the beam problem of the secondary cell, theterminal may be controlled to perform a contention-based RA procedure inthe primary cell or the secondary cell. For example, when the receptionstrength of the reference signal of the beam is equal to or greater thana reference value, the terminal may perform a non-contention-based RAprocedure. On the other hand, when the reception strength of thereference signal of the beam is less than a reference value, thenon-contention-based RA procedure may be restricted. Here, the referencecondition for the non-contention-based RA procedure may be defined as athreshold value for the reception strength of the reference signal ofthe beam. The reception strength of the reference signal (e.g., SS/PBCHblock, CSI-RS, PT-RS, DMRS, etc.) may be represented as RSSI, RSRP, orRSRQ.

Also, a timer indicating an interval (or duration) during which anon-contention-based RA procedure for beam recovery may be performed maybe configured. When the non-contention-based RA procedure has not beensuccessfully completed before expiration of the timer, the terminal maybe controlled to perform a contention-based RA procedure.

When a contention-based RA procedure for beam recovery is performed theterminal may transmit a control message including at least one of anidentifier of a cell performing the beam problem detection operation orthe beam recovery operation, information for identifying thecorresponding beam (e.g., the beam in which the problem is detected), ameasurement result of the corresponding beam, a measurement result of acandidate beam, information indicating whether or not a condition forperforming a non-contention-based RA procedure is satisfied, informationindicating the inactivation of the cell (e.g., the cell in which thebeam problem is detected), and a time elapsed from a time point at whichthe beam problem is detected (or, the initiation time of the beamrecovery operation).

In the case that the secondary cell in which the beam problem isdetected has been, inactivated, the inactivated secondary cell may beactivated again when the beam recovery operation for the secondary cellis completed. When the beam recovery is completed by the secondarycell's beam monitoring or measurement result instead of performing theRA procedure in the secondary cell or the transmission of the controlmessage for beam recovery, the terminal may report informationindicating completion of the beam recovery for the secondary cell to theprimary cell. Upon receiving the information indicating that beamrecovery for the secondary cell has been completed from the terminal,the primary cell may activate the secondary cell indicated by theinformation received from the terminal, and transmit control informationfor the activated secondary cell to at least one of the correspondingsecondary cell and the terminal.

The cells supporting the independent beam management operation and theCA function may perform additional operations for the beam managementoperation of the primary cell. For example, when a beam problem of theprimary cell is detected according to the beam management operation, theterminal may transmit information indicating that the beam problem ofthe primary cell has been detected before performing the beam failuredeclaration operation or the beam recovery operation. In this case, theterminal may transmit information for identifying the beam (e.g., thebeam in which the problem is detected) of the primary cell, ameasurement result of the beam, a measurement result of a candidatebeam, information indicating whether or not a condition for performing anon-contention-based RA procedure is satisfied, a time elapsed from thetime when the beam problem is detected (or, the initiation time of thebeam recovery operation), and the like by applying the above-describedconfiguration parameters.

As another method, when the beam problem is detected in the primarycell, the terminal may perform the beam recovery operation beforeexpiration of a timer for a beam recovery operation of a primary cell(e.g., T_(BR)). In the case that a beam failure is declared as a resultof the beam recovery operation for the primary cell, the terminal maytransmit to the secondary cell a control message including informationindicating that the beam failure has been declared at the time of thebeam failure declaration.

When the control message indicating the detection of the beam problem ofthe primary cell, the beam recovery operation, the beam recoveryfailure, or the beam failure declaration is received from the terminal,the secondary cell may transmit the control message received from theterminal to the primary cell. When the control information indicatingthe occurrence of the problem with respect to the beam managementoperation is received from the secondary cell, the primary cell may stoptransmission of packets to the terminal before receiving a controlmessage indicating that the beam recovery operation has beensuccessfully completed from the terminal. Also, the primary cell maytransmit control information, reference signals, and the like for beamrecovery to the terminal using a configured beam other than the servingbeam of the terminal.

When there is not an RA attempt or a reception of information indicatingthat the beam recovery operation has been successfully completed withina period configured in consideration of the elapsed time from the beamproblem detection, or a period configured regardless of the elapsedtime, the primary cell may declare an RLF for the terminal. Also, theprimary cell may determine the operational state of the terminal to bethe RRC_INACTIVE state or the RRC_IDLE state, and release the connectionwith the terminal. Also, the primary cell may perform a connectionreconfiguration procedure or a handover procedure for changing thesecondary cell to a new primary cell.

When a connection reconfiguration procedure or a handover procedure forchanging the secondary cell to a primary cell is performed due to thebeam recovery failure of the primary cell (or, a failure of radio linkrecovery), the primary cell may transmit RRC context information (e.g.,access stratum (AS) context information) to the secondary cell. Uponreceiving the RRC context information of the terminal from the primarycell, the secondary cell may inform the terminal that the secondary cellhas been changed to a primary cell by transmitting the RRC contextinformation of the terminal to the terminal. That is, a control messageindicating that the secondary cell has been changed to a new primarycell, or a control message for connection reconfiguration, whichincludes control information related to the change between the secondarycell and the primary cell, may be transmitted to the terminal.

Upon receiving the control message indicating that the secondary cellhas been changed to a primary cell due to the beam recovery failure (or,radio link recovery failure) of the primary cell from the secondarycell, the terminal may delete the configuration parameters for theprevious primary cell, and may reconfigure related parameters using thecontrol message (e.g., control message for connection reconfiguration)received from the secondary cell.

The above-described beam or radio link management operation in a radioaccess section (e.g., access link) between the terminal and the basestation may be applied to the beam or radio link management operationfor the mobile XDU in the Xhaul network. The above-described functionand role of the base station (e.g., the base stations 110-1 to 110-3 inFIG. 1, the base stations 320 and 330 in FIG. 3, the base stations 530and 540 in FIG. 5, or the like), the above-described function and roleof the RRH performing some functions of the radio protocol of the basestation, or the above-described function and role of the TRP (e.g., theTRPs 350-1 and 350-2 in FIG. 3, the TRP 430 in FIG. 4, the TRP 550 inFIG. 5, or the like) performing some functions of the radio protocol ofthe base station may be performed by the XDUs (e.g., the serving XDU,the linking XDUs, the candidate linking XDUs, the target XDU, thecandidate target XDU, or the like) other than the mobile XDU. Thefunction and role of the terminal may be performed by the mobile XDU.The function and role of the XCU may be performed by an entity (e.g.,the RRC layer of the LTE system) that supports radio resource controlfunctions of the base station.

In the above-described embodiments, even when each of start, stop,reset, restart, and expiration of the defined timer is not describeddiscriminately, each of start, stop, reset, restart, and expiration maymean the operation of the timer or the operation of the counter for thetimer.

In the above-described embodiments, each of the cell and the basestation may refer to a Node B, an evolved Node B (eNB), a basetransceiver station (BTS), a radio base station, a radio transceiver, anaccess point (AP), an access node, a roadside unit (RSU), a radio remotehead (RRH), a transmission point (TP), a transmission and receptionpoint (TRP), a gNB, or the like.

Also, in the above-described embodiments, the terminal may refer to aterminal, an access terminal, a mobile terminal, a station, a subscriberstation, a mobile station, a portable subscriber station, a node, adevice, an Internet of Thing (IoT) device, a mountedmodule/device/terminal, an on-board device (OBD), an on-board terminal(OBT), or the like.

The embodiments of the present disclosure may be implemented as programinstructions executable by a variety of computers and recorded on acomputer readable medium. The computer readable medium may include aprogram instruction, a data file, a data structure, or a combinationthereof. The program instructions recorded on the computer readablemedium may be designed and configured specifically for the presentdisclosure or can be publicly known and available to those who areskilled in the field of computer software.

Examples of the computer readable medium may include a hardware devicesuch as ROM, RAM, and flash memory, which are specifically configured tostore and execute the program instructions. Examples of the programinstructions include machine codes made by, for example, a compiler, aswell as high-level language codes executable by a computer, using aninterpreter. The above exemplary hardware device can be configured tooperate as at least one software module in order to perform theembodiments of the present disclosure, and vice versa.

While the embodiments of the present disclosure and their advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations may be made herein withoutdeparting from the scope of the present disclosure.

What is claimed is:
 1. An operation method performed by a terminal in acommunication system, the operation method comprising: configuring oneor more cells with a base station; performing a measurement operationfor one or more candidate beams of a first cell among the one or morecells; generating a medium access control (MAC) control element (CE)including an indication information of the first cell and an indicationinformation of at least one candidate beam which is selected based onresults of the measurement operation among the one or more candidatebeams; and transmitting the MAC CE to the base station, wherein the oneor more candidate beams are configured by the base station, and the MACCE is used for beam failure recovery (BFR).
 2. The operation methodaccording to claim 1, wherein the MAC CE further includes measurementinformation of the one or more candidate beams.
 3. The operation methodaccording to claim 1, wherein, when the first cell is a secondary cellof the base station, the MAC CE for the secondary cell is transmitted ina primary cell among the one or more cells of the base station.
 4. Theoperation method according to claim 3, wherein the MAC CE indicates toinactive the secondary cell.
 5. The operation method according to claim1, wherein resource information of a random access (RA) procedure forthe BFR is received from the base station.
 6. The operation methodaccording to claim 5, wherein the resource information includes at leastone of a RA preamble index, masking information, a preamble format of aphysical random access channel (PRACH), and time-frequency resources ofthe PRACH.
 7. The operation method according to claim 5, furthercomprising: when beam failure is detected in the first cell and thefirst cell is a primary cell of the base station, performing the RAprocedure in the primary cell, wherein the RA procedure is acontention-based RA procedure or a non-contention-based RA procedure. 8.The operation method according to claim 7, wherein: when a referencesignal received power (RSRP) in the primary cell is greater than orequal to a threshold, the non-contention-based RA procedure isperformed, and when the RSRP in the primary cell is lower than thethreshold, the contention-based RA procedure is performed.
 9. Theoperation method according to claim 7, wherein: the non-contention-basedRA procedure is performed in a time period corresponding a timer, andwhen the non-contention-based RA procedure is not completed in the timeperiod, the contention-based RA procedure is performed after the timeperiod.